compat/zlib/contrib/dotzlib/DotZLib/UnitTests.cs
compat/zlib/contrib/vstudio/readme.txt
compat/zlib/contrib/vstudio/*/zlib.rc
compat/zlib/win32/*.txt
compat/zlib/win64/*.txt



tools/tcl.hpj.in
tools/tcl.wse.in
win/buildall.vc.bat
win/coffbase.txt
win/makefile.bc
win/makefile.vc
win/rules.vc


win/tcl.dsp
win/tcl.dsw
win/tcl.hpj.in

tools/tcl.hpj.in
tools/tcl.wse.in
win/buildall.vc.bat
win/coffbase.txt
win/makefile.bc
win/makefile.vc
win/rules.vc
win/tcl.dsp
win/tcl.dsw
win/tcl.hpj.in

*/config.cache
*/config.log
*/config.status
*/tclConfig.sh
*/tclsh*
*/tcltest*
*/versions.vc

html
libtommath/bn.ilg
libtommath/bn.ind
libtommath/pretty.build
libtommath/tommath.src

libtommath/*.pdf
libtommath/*.pl
libtommath/*.sh

libtommath/tombc/*
libtommath/pre_gen/*
libtommath/pics/*
libtommath/mtest/*
libtommath/logs/*
libtommath/etc/*
libtommath/demo/*
libtommath/*.out
libtommath/*.tex
unix/autoMkindex.tcl
unix/dltest.marker
unix/tcl.pc
unix/tclIndex
unix/pkgs/*
win/Debug_VC*
win/Release_VC*
win/pkgs/*
win/tcl.hpj

<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
	<name>tcl8.7</name>
	<comment></comment>
	<projects>
	</projects>
	<buildSpec>
	</buildSpec>
	<natures>
	</natures>

A NOTE ON THE CHANGELOG:
Starting in early 2011, Tcl source code has been under the management of
fossil, hosted at http://core.tcl.tk/tcl/ .  Fossil presents a "Timeline"
view of changes made that is superior in every way to a hand edited log file.
Because of this, many Tcl developers are now out of the habit of maintaining
this log file.  You may still find useful things in it, but the Timeline is
a better first place to look now.
============================================================================

2013-09-19  Don Porter  <dgp@users.sourceforge.net>

README:  Tcl
    This is the Tcl 8.7a0 source distribution.
	http://sourceforge.net/projects/tcl/files/Tcl/
    You can get any source release of Tcl from the URL above.

Contents
--------
    1. Introduction
    2. Documentation

Tcl can also be used for a variety of web-related tasks and for creating
powerful command languages for applications.

Tcl is maintained, enhanced, and distributed freely by the Tcl community.
Source code development and tracking of bug reports and feature requests
takes place at:

	http://core.tcl.tk/

Tcl/Tk release and mailing list services are hosted by SourceForge:

	http://sourceforge.net/projects/tcl/

with the Tcl Developer Xchange hosted at:

	http://www.tcl.tk/

Tcl is a freely available open source package.  You can do virtually
anything you like with it, such as modifying it, redistributing it,
and selling it either in whole or in part.  See the file
"license.terms" for complete information.

2. Documentation
----------------

Extensive documentation is available at our website.
The home page for this release, including new features, is
	http://www.tcl.tk/software/tcltk/8.7.html

Detailed release notes can be found at the file distributions page
by clicking on the relevant version.
	http://sourceforge.net/projects/tcl/files/Tcl/

Information about Tcl itself can be found at
	http://www.tcl.tk/about/

There have been many Tcl books on the market.  Many are mentioned in the Wiki:
	http://wiki.tcl.tk/_/ref?N=25206

To view the complete set of reference manual entries for Tcl 8.7 online,
visit the URL:
	http://www.tcl.tk/man/tcl8.7/

2a. Unix Documentation
----------------------

The "doc" subdirectory in this release contains a complete set of
reference manual entries for Tcl.  Files with extension ".1" are for
programs (for example, tclsh.1); files with extension ".3" are for C

3. Compiling and installing Tcl
-------------------------------

There are brief notes in the unix/README, win/README, and macosx/README about
compiling on these different platforms.  There is additional information
about building Tcl from sources at

	http://www.tcl.tk/doc/howto/compile.html

4. Development tools
---------------------------

ActiveState produces a high quality set of commercial quality development
tools that is available to accelerate your Tcl application development.
Tcl Dev Kit builds on the earlier TclPro toolset and provides a debugger,

see the "Support and bug fixes" section below.

6. Tcl'ers Wiki
---------------

A Wiki-based open community site covering all aspects of Tcl/Tk is at:

	http://wiki.tcl.tk/

It is dedicated to the Tcl programming language and its extensions.  A
wealth of useful information can be found there.  It contains code
snippets, references to papers, books, and FAQs, as well as pointers to
development tools, extensions, and applications.  You can also recommend
additional URLs by editing the wiki yourself.

8. Support and Training
------------------------

We are very interested in receiving bug reports, patches, and suggestions
for improvements.  We prefer that you send this information to us as
tickets entered into our tracker at:

	http://core.tcl.tk/tcl/reportlist

We will log and follow-up on each bug, although we cannot promise a
specific turn-around time.  Enhancements may take longer and may not happen
at all unless there is widespread support for them (we're trying to
slow the rate at which Tcl/Tk turns into a kitchen sink).  It's very
difficult to make incompatible changes to Tcl/Tk at this point, due to
the size of the installed base.

The Tcl community is too large for us to provide much individual support
for users.  If you need help we suggest that you post questions to
comp.lang.tcl.  We read the newsgroup and will attempt to answer esoteric
questions for which no one else is likely to know the answer.  In addition,
see the following Web site for links to other organizations that offer
Tcl/Tk training:

	http://wiki.tcl.tk/training

9. Tracking Development
-----------------------

Tcl is developed in public.  To keep an eye on how Tcl is changing, see
	http://core.tcl.tk/

10. Thank You
-------------

We'd like to express our thanks to the Tcl community for all the
helpful suggestions, bug reports, and patches we have received.
Tcl/Tk has improved vastly and will continue to do so with your help.

2016-02-03 (bug)[25842c] stream [zlib deflate] fails with 0 input (ade,fellows)

2016-02-04 (bug)[3d96b7][593baa][cf74de] crashes in OO teardown (porter,fellows)

2016-02-22 (bug)[9b4702] [info exists env(missing)] kills trace (nijtmans)

--- Released 8.6.5, February 29, 2016 --- http://core.tcl.tk/tcl/ for details

/*
 * fixstrtod.c --
 *
 *	Source code for the "fixstrtod" procedure.  This procedure is
 *	used in place of strtod under Solaris 2.4, in order to fix
 *	a bug where the "end" pointer gets set incorrectly.
 *
 * Copyright (c) 1995 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include <stdio.h>

#undef strtod

/*
 * Declare strtod explicitly rather than including stdlib.h, since in
 * somes systems (e.g. SunOS 4.1.4) stdlib.h doesn't declare strtod.
 */

extern double strtod(char *, char **);

double
fixstrtod(
    char *string,
    char **endPtr)
{
    double d;
    d = strtod(string, endPtr);
    if ((endPtr != NULL) && (*endPtr != string) && ((*endPtr)[-1] == 0)) {
	*endPtr -= 1;
    }
    return d;
}

void
closedir(
    register DIR *dirp)
{
    close(dirp->dd_fd);
    dirp->dd_fd = -1;
    dirp->dd_loc = 0;
    ckfree(dirp);
}

extern void		exit(int status);
extern int		free(char *blockPtr);
extern char *		getenv(const char *name);
extern char *		malloc(unsigned int numBytes);
extern void		qsort(void *base, int n, int size, int (*compar)(
			    const void *element1, const void *element2));
extern char *		realloc(char *ptr, unsigned int numBytes);
extern double		strtod(const char *string, char **endPtr);
extern long		strtol(const char *string, char **endPtr, int base);
extern unsigned long	strtoul(const char *string, char **endPtr, int base);

#endif /* _STDLIB */

/*
 * strtod.c --
 *
 *	Source code for the "strtod" library procedure.
 *
 * Copyright (c) 1988-1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"

#ifndef TRUE
#define TRUE 1
#define FALSE 0
#endif
#ifndef NULL
#define NULL 0
#endif

static const int maxExponent = 511;	/* Largest possible base 10 exponent.  Any
				 * exponent larger than this will already
				 * produce underflow or overflow, so there's
				 * no need to worry about additional digits.
				 */
static const double powersOf10[] = {	/* Table giving binary powers of 10.  Entry */
    10.,			/* is 10^2^i.  Used to convert decimal */
    100.,			/* exponents into floating-point numbers. */
    1.0e4,
    1.0e8,
    1.0e16,
    1.0e32,
    1.0e64,
    1.0e128,
    1.0e256
};

/*
 *----------------------------------------------------------------------
 *
 * strtod --
 *
 *	This procedure converts a floating-point number from an ASCII
 *	decimal representation to internal double-precision format.
 *
 * Results:
 *	The return value is the double-precision floating-point
 *	representation of the characters in string.  If endPtr isn't
 *	NULL, then *endPtr is filled in with the address of the
 *	next character after the last one that was part of the
 *	floating-point number.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

double
strtod(
    const char *string,		/* A decimal ASCII floating-point number,
				 * optionally preceded by white space. Must
				 * have form "-I.FE-X", where I is the integer
				 * part of the mantissa, F is the fractional
				 * part of the mantissa, and X is the
				 * exponent. Either of the signs may be "+",
				 * "-", or omitted. Either I or F may be
				 * omitted, or both. The decimal point isn't
				 * necessary unless F is present. The "E" may
				 * actually be an "e". E and X may both be
				 * omitted (but not just one). */
    char **endPtr)		/* If non-NULL, store terminating character's
				 * address here. */
{
    int sign, expSign = FALSE;
    double fraction, dblExp;
    const double *d;
    register const char *p;
    register int c;
    int exp = 0;		/* Exponent read from "EX" field. */
    int fracExp = 0;		/* Exponent that derives from the fractional
				 * part. Under normal circumstatnces, it is
				 * the negative of the number of digits in F.
				 * However, if I is very long, the last digits
				 * of I get dropped (otherwise a long I with a
				 * large negative exponent could cause an
				 * unnecessary overflow on I alone). In this
				 * case, fracExp is incremented one for each
				 * dropped digit. */
    int mantSize;		/* Number of digits in mantissa. */
    int decPt;			/* Number of mantissa digits BEFORE decimal
				 * point. */
    const char *pExp;		/* Temporarily holds location of exponent in
				 * string. */

    /*
     * Strip off leading blanks and check for a sign.
     */

    p = string;
    while (isspace(UCHAR(*p))) {
	p += 1;
    }
    if (*p == '-') {
	sign = TRUE;
	p += 1;
    } else {
	if (*p == '+') {
	    p += 1;
	}
	sign = FALSE;
    }

    /*
     * Count the number of digits in the mantissa (including the decimal
     * point), and also locate the decimal point.
     */

    decPt = -1;
    for (mantSize = 0; ; mantSize += 1)
    {
	c = *p;
	if (!isdigit(c)) {
	    if ((c != '.') || (decPt >= 0)) {
		break;
	    }
	    decPt = mantSize;
	}
	p += 1;
    }

    /*
     * Now suck up the digits in the mantissa. Use two integers to collect 9
     * digits each (this is faster than using floating-point). If the mantissa
     * has more than 18 digits, ignore the extras, since they can't affect the
     * value anyway.
     */

    pExp  = p;
    p -= mantSize;
    if (decPt < 0) {
	decPt = mantSize;
    } else {
	mantSize -= 1;		/* One of the digits was the point. */
    }
    if (mantSize > 18) {
	fracExp = decPt - 18;
	mantSize = 18;
    } else {
	fracExp = decPt - mantSize;
    }
    if (mantSize == 0) {
	fraction = 0.0;
	p = string;
	goto done;
    } else {
	int frac1, frac2;

	frac1 = 0;
	for ( ; mantSize > 9; mantSize -= 1) {
	    c = *p;
	    p += 1;
	    if (c == '.') {
		c = *p;
		p += 1;
	    }
	    frac1 = 10*frac1 + (c - '0');
	}
	frac2 = 0;
	for (; mantSize > 0; mantSize -= 1) {
	    c = *p;
	    p += 1;
	    if (c == '.') {
		c = *p;
		p += 1;
	    }
	    frac2 = 10*frac2 + (c - '0');
	}
	fraction = (1.0e9 * frac1) + frac2;
    }

    /*
     * Skim off the exponent.
     */

    p = pExp;
    if ((*p == 'E') || (*p == 'e')) {
	p += 1;
	if (*p == '-') {
	    expSign = TRUE;
	    p += 1;
	} else {
	    if (*p == '+') {
		p += 1;
	    }
	    expSign = FALSE;
	}
	if (!isdigit(UCHAR(*p))) {
	    p = pExp;
	    goto done;
	}
	while (isdigit(UCHAR(*p))) {
	    exp = exp * 10 + (*p - '0');
	    p += 1;
	}
    }
    if (expSign) {
	exp = fracExp - exp;
    } else {
	exp = fracExp + exp;
    }

    /*
     * Generate a floating-point number that represents the exponent. Do this
     * by processing the exponent one bit at a time to combine many powers of
     * 2 of 10. Then combine the exponent with the fraction.
     */

    if (exp < 0) {
	expSign = TRUE;
	exp = -exp;
    } else {
	expSign = FALSE;
    }
    if (exp > maxExponent) {
	exp = maxExponent;
	errno = ERANGE;
    }
    dblExp = 1.0;
    for (d = powersOf10; exp != 0; exp >>= 1, ++d) {
	if (exp & 01) {
	    dblExp *= *d;
	}
    }
    if (expSign) {
	fraction /= dblExp;
    } else {
	fraction *= dblExp;
    }

  done:
    if (endPtr != NULL) {
	*endPtr = (char *) p;
    }

    if (sign) {
	return -fraction;
    }
    return fraction;
}

    long result;

    /*
     * Skip any leading blanks.
     */

    p = string;
    while (isspace(UCHAR(*p))) {
	p += 1;
    }

    /*
     * Check for a sign.
     */

    int overflow=0;

    /*
     * Skip any leading blanks.
     */

    p = string;
    while (isspace(UCHAR(*p))) {
	p += 1;
    }
    if (*p == '-') {
        negative = 1;
        p += 1;
    } else {
        if (*p == '+') {

	result = waitPtr->pid;
	*statusPtr = *((int *) &waitPtr->status);
	if (prevPtr == NULL) {
	    deadList = waitPtr->nextPtr;
	} else {
	    prevPtr->nextPtr = waitPtr->nextPtr;
	}
	ckfree(waitPtr);
	return result;
    }

    /*
     * Wait for any process to stop or exit. If it's an acceptable one then
     * return it to the caller; otherwise store information about it in the
     * list of exited processes and try again. On systems that have only wait

                      0,NULL,OPEN_EXISTING,0,NULL);
  GetFileTime(hFile,&ftCreate,&ftLastAcc,&ftLastWrite);
  DosDateTimeToFileTime((WORD)(dosdate>>16),(WORD)dosdate,&ftLocal);
  LocalFileTimeToFileTime(&ftLocal,&ftm);
  SetFileTime(hFile,&ftm,&ftLastAcc,&ftm);
  CloseHandle(hFile);
#else
#ifdef unix || __APPLE__
  struct utimbuf ut;
  struct tm newdate;
  newdate.tm_sec = tmu_date.tm_sec;
  newdate.tm_min=tmu_date.tm_min;
  newdate.tm_hour=tmu_date.tm_hour;
  newdate.tm_mday=tmu_date.tm_mday;
  newdate.tm_mon=tmu_date.tm_mon;

        FindClose(hFind);
        ret = 1;
      }
  }
  return ret;
}
#else
#ifdef unix || __APPLE__
uLong filetime(f, tmzip, dt)
    char *f;               /* name of file to get info on */
    tm_zip *tmzip;         /* return value: access, modific. and creation times */
    uLong *dt;             /* dostime */
{
  int ret=0;
  struct stat s;        /* results of stat() */

1. Compression algorithm (deflate)

The deflation algorithm used by gzip (also zip and zlib) is a variation of
LZ77 (Lempel-Ziv 1977, see reference below). It finds duplicated strings in
the input data.  The second occurrence of a string is replaced by a
pointer to the previous string, in the form of a pair (distance,
length).  Distances are limited to 32K bytes, and lengths are limited
to 258 bytes. When a string does not occur anywhere in the previous
32K bytes, it is emitted as a sequence of literal bytes.  (In this
description, `string' must be taken as an arbitrary sequence of bytes,
and is not restricted to printable characters.)

Literals or match lengths are compressed with one Huffman tree, and
match distances are compressed with another tree. The trees are stored
in a compact form at the start of each block. The blocks can have any
size (except that the compressed data for one block must fit in
available memory). A block is terminated when deflate() determines that
it would be useful to start another block with fresh trees. (This is
somewhat similar to the behavior of LZW-based _compress_.)

Duplicated strings are found using a hash table. All input strings of
length 3 are inserted in the hash table. A hash index is computed for
the next 3 bytes. If the hash chain for this index is not empty, all
strings in the chain are compared with the current input string, and
the longest match is selected.

The hash chains are searched starting with the most recent strings, to
favor small distances and thus take advantage of the Huffman encoding.
The hash chains are singly linked. There are no deletions from the
hash chains, the algorithm simply discards matches that are too old.

To avoid a worst-case situation, very long hash chains are arbitrarily
truncated at a certain length, determined by a runtime option (level
parameter of deflateInit). So deflate() does not always find the longest
possible match but generally finds a match which is long enough.

deflate() also defers the selection of matches with a lazy evaluation
mechanism. After a match of length N has been found, deflate() searches for
a longer match at the next input byte. If a longer match is found, the
previous match is truncated to a length of one (thus producing a single
literal byte) and the process of lazy evaluation begins again. Otherwise,
the original match is kept, and the next match search is attempted only N
steps later.

The lazy match evaluation is also subject to a runtime parameter. If
the current match is long enough, deflate() reduces the search for a longer
match, thus speeding up the whole process. If compression ratio is more
important than speed, deflate() attempts a complete second search even if
the first match is already long enough.

The lazy match evaluation is not performed for the fastest compression
modes (level parameter 1 to 3). For these fast modes, new strings
are inserted in the hash table only when no match was found, or
when the match is not too long. This degrades the compression ratio
but saves time since there are both fewer insertions and fewer searches.


2. Decompression algorithm (inflate)

2.1 Introduction

The key question is how to represent a Huffman code (or any prefix code) so
that you can decode fast.  The most important characteristic is that shorter
codes are much more common than longer codes, so pay attention to decoding the
short codes fast, and let the long codes take longer to decode.

inflate() sets up a first level table that covers some number of bits of
input less than the length of longest code.  It gets that many bits from the
stream, and looks it up in the table.  The table will tell if the next
code is that many bits or less and how many, and if it is, it will tell
the value, else it will point to the next level table for which inflate()
grabs more bits and tries to decode a longer code.

How many bits to make the first lookup is a tradeoff between the time it
takes to decode and the time it takes to build the table.  If building the
table took no time (and if you had infinite memory), then there would only
be a first level table to cover all the way to the longest code.  However,
building the table ends up taking a lot longer for more bits since short
codes are replicated many times in such a table.  What inflate() does is
simply to make the number of bits in the first table a variable, and  then
to set that variable for the maximum speed.

For inflate, which has 286 possible codes for the literal/length tree, the size
of the first table is nine bits.  Also the distance trees have 30 possible
values, and the size of the first table is six bits.  Note that for each of
those cases, the table ended up one bit longer than the ``average'' code
length, i.e. the code length of an approximately flat code which would be a
little more than eight bits for 286 symbols and a little less than five bits
for 30 symbols.


2.2 More details on the inflate table lookup

Ok, you want to know what this cleverly obfuscated inflate tree actually
looks like.  You are correct that it's not a Huffman tree.  It is simply a
lookup table for the first, let's say, nine bits of a Huffman symbol.  The
symbol could be as short as one bit or as long as 15 bits.  If a particular
symbol is shorter than nine bits, then that symbol's translation is duplicated
in all those entries that start with that symbol's bits.  For example, if the
symbol is four bits, then it's duplicated 32 times in a nine-bit table.  If a
symbol is nine bits long, it appears in the table once.

If the symbol is longer than nine bits, then that entry in the table points
to another similar table for the remaining bits.  Again, there are duplicated
entries as needed.  The idea is that most of the time the symbol will be short
and there will only be one table look up.  (That's whole idea behind data
compression in the first place.)  For the less frequent long symbols, there
will be two lookups.  If you had a compression method with really long
symbols, you could have as many levels of lookups as is efficient.  For
inflate, two is enough.

So a table entry either points to another table (in which case nine bits in
the above example are gobbled), or it contains the translation for the symbol
and the number of bits to gobble.  Then you start again with the next
ungobbled bit.

You may wonder: why not just have one lookup table for how ever many bits the
longest symbol is?  The reason is that if you do that, you end up spending
more time filling in duplicate symbol entries than you do actually decoding.
At least for deflate's output that generates new trees every several 10's of
kbytes.  You can imagine that filling in a 2^15 entry table for a 15-bit code
would take too long if you're only decoding several thousand symbols.  At the
other extreme, you could make a new table for every bit in the code.  In fact,
that's essentially a Huffman tree.  But then you spend too much time
traversing the tree while decoding, even for short symbols.

So the number of bits for the first lookup table is a trade of the time to
fill out the table vs. the time spent looking at the second level and above of
the table.

Here is an example, scaled down:

The code being decoded, with 10 symbols, from 1 to 6 bits long:

A: 0
B: 10
C: 1100
D: 11010
E: 11011
F: 11100
G: 11101
H: 11110
I: 111110
J: 111111

Let's make the first table three bits long (eight entries):

000: A,1
001: A,1
010: A,1
011: A,1
100: B,2
101: B,2
110: -> table X (gobble 3 bits)
111: -> table Y (gobble 3 bits)

Each entry is what the bits decode as and how many bits that is, i.e. how
many bits to gobble.  Or the entry points to another table, with the number of
bits to gobble implicit in the size of the table.

Table X is two bits long since the longest code starting with 110 is five bits
long:

00: C,1
01: C,1
10: D,2
11: E,2

Table Y is three bits long since the longest code starting with 111 is six
bits long:

000: F,2
001: F,2
010: G,2
011: G,2
100: H,2
101: H,2
110: I,3
111: J,3

So what we have here are three tables with a total of 20 entries that had to
be constructed.  That's compared to 64 entries for a single table.  Or
compared to 16 entries for a Huffman tree (six two entry tables and one four
entry table).  Assuming that the code ideally represents the probability of
the symbols, it takes on the average 1.25 lookups per symbol.  That's compared
to one lookup for the single table, or 1.66 lookups per symbol for the
Huffman tree.

There, I think that gives you a picture of what's going on.  For inflate, the
meaning of a particular symbol is often more than just a letter.  It can be a
byte (a "literal"), or it can be either a length or a distance which
indicates a base value and a number of bits to fetch after the code that is
added to the base value.  Or it might be the special end-of-block code.  The
data structures created in inftrees.c try to encode all that information
compactly in the tables.


Jean-loup Gailly        Mark Adler
jloup@gzip.org          madler@alumni.caltech.edu


References:

[LZ77] Ziv J., Lempel A., ``A Universal Algorithm for Sequential Data
Compression,'' IEEE Transactions on Information Theory, Vol. 23, No. 3,
pp. 337-343.

``DEFLATE Compressed Data Format Specification'' available in
http://tools.ietf.org/html/rfc1951

Network Working Group                                         P. Deutsch
Request for Comments: 1950                           Aladdin Enterprises
Category: Informational                                      J-L. Gailly
                                                                Info-ZIP
                                                                May 1996


         ZLIB Compressed Data Format Specification version 3.3

Status of This Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

IESG Note:

   The IESG takes no position on the validity of any Intellectual
   Property Rights statements contained in this document.

Notices

   Copyright (c) 1996 L. Peter Deutsch and Jean-Loup Gailly

   Permission is granted to copy and distribute this document for any
   purpose and without charge, including translations into other
   languages and incorporation into compilations, provided that the
   copyright notice and this notice are preserved, and that any
   substantive changes or deletions from the original are clearly
   marked.

   A pointer to the latest version of this and related documentation in
   HTML format can be found at the URL
   <ftp://ftp.uu.net/graphics/png/documents/zlib/zdoc-index.html>.

Abstract

   This specification defines a lossless compressed data format.  The
   data can be produced or consumed, even for an arbitrarily long
   sequentially presented input data stream, using only an a priori
   bounded amount of intermediate storage.  The format presently uses
   the DEFLATE compression method but can be easily extended to use
   other compression methods.  It can be implemented readily in a manner
   not covered by patents.  This specification also defines the ADLER-32
   checksum (an extension and improvement of the Fletcher checksum),
   used for detection of data corruption, and provides an algorithm for
   computing it.




Deutsch & Gailly             Informational                      [Page 1]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


Table of Contents

   1. Introduction ................................................... 2
      1.1. Purpose ................................................... 2
      1.2. Intended audience ......................................... 3
      1.3. Scope ..................................................... 3
      1.4. Compliance ................................................ 3
      1.5.  Definitions of terms and conventions used ................ 3
      1.6. Changes from previous versions ............................ 3
   2. Detailed specification ......................................... 3
      2.1. Overall conventions ....................................... 3
      2.2. Data format ............................................... 4
      2.3. Compliance ................................................ 7
   3. References ..................................................... 7
   4. Source code .................................................... 8
   5. Security Considerations ........................................ 8
   6. Acknowledgements ............................................... 8
   7. Authors' Addresses ............................................. 8
   8. Appendix: Rationale ............................................ 9
   9. Appendix: Sample code ..........................................10

1. Introduction

   1.1. Purpose

      The purpose of this specification is to define a lossless
      compressed data format that:

          * Is independent of CPU type, operating system, file system,
            and character set, and hence can be used for interchange;

          * Can be produced or consumed, even for an arbitrarily long
            sequentially presented input data stream, using only an a
            priori bounded amount of intermediate storage, and hence can
            be used in data communications or similar structures such as
            Unix filters;

          * Can use a number of different compression methods;

          * Can be implemented readily in a manner not covered by
            patents, and hence can be practiced freely.

      The data format defined by this specification does not attempt to
      allow random access to compressed data.







Deutsch & Gailly             Informational                      [Page 2]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


   1.2. Intended audience

      This specification is intended for use by implementors of software
      to compress data into zlib format and/or decompress data from zlib
      format.

      The text of the specification assumes a basic background in
      programming at the level of bits and other primitive data
      representations.

   1.3. Scope

      The specification specifies a compressed data format that can be
      used for in-memory compression of a sequence of arbitrary bytes.

   1.4. Compliance

      Unless otherwise indicated below, a compliant decompressor must be
      able to accept and decompress any data set that conforms to all
      the specifications presented here; a compliant compressor must
      produce data sets that conform to all the specifications presented
      here.

   1.5.  Definitions of terms and conventions used

      byte: 8 bits stored or transmitted as a unit (same as an octet).
      (For this specification, a byte is exactly 8 bits, even on
      machines which store a character on a number of bits different
      from 8.) See below, for the numbering of bits within a byte.

   1.6. Changes from previous versions

      Version 3.1 was the first public release of this specification.
      In version 3.2, some terminology was changed and the Adler-32
      sample code was rewritten for clarity.  In version 3.3, the
      support for a preset dictionary was introduced, and the
      specification was converted to RFC style.

2. Detailed specification

   2.1. Overall conventions

      In the diagrams below, a box like this:

         +---+
         |   | <-- the vertical bars might be missing
         +---+




Deutsch & Gailly             Informational                      [Page 3]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


      represents one byte; a box like this:

         +==============+
         |              |
         +==============+

      represents a variable number of bytes.

      Bytes stored within a computer do not have a "bit order", since
      they are always treated as a unit.  However, a byte considered as
      an integer between 0 and 255 does have a most- and least-
      significant bit, and since we write numbers with the most-
      significant digit on the left, we also write bytes with the most-
      significant bit on the left.  In the diagrams below, we number the
      bits of a byte so that bit 0 is the least-significant bit, i.e.,
      the bits are numbered:

         +--------+
         |76543210|
         +--------+

      Within a computer, a number may occupy multiple bytes.  All
      multi-byte numbers in the format described here are stored with
      the MOST-significant byte first (at the lower memory address).
      For example, the decimal number 520 is stored as:

             0     1
         +--------+--------+
         |00000010|00001000|
         +--------+--------+
          ^        ^
          |        |
          |        + less significant byte = 8
          + more significant byte = 2 x 256

   2.2. Data format

      A zlib stream has the following structure:

           0   1
         +---+---+
         |CMF|FLG|   (more-->)
         +---+---+








Deutsch & Gailly             Informational                      [Page 4]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


      (if FLG.FDICT set)

           0   1   2   3
         +---+---+---+---+
         |     DICTID    |   (more-->)
         +---+---+---+---+

         +=====================+---+---+---+---+
         |...compressed data...|    ADLER32    |
         +=====================+---+---+---+---+

      Any data which may appear after ADLER32 are not part of the zlib
      stream.

      CMF (Compression Method and flags)
         This byte is divided into a 4-bit compression method and a 4-
         bit information field depending on the compression method.

            bits 0 to 3  CM     Compression method
            bits 4 to 7  CINFO  Compression info

      CM (Compression method)
         This identifies the compression method used in the file. CM = 8
         denotes the "deflate" compression method with a window size up
         to 32K.  This is the method used by gzip and PNG (see
         references [1] and [2] in Chapter 3, below, for the reference
         documents).  CM = 15 is reserved.  It might be used in a future
         version of this specification to indicate the presence of an
         extra field before the compressed data.

      CINFO (Compression info)
         For CM = 8, CINFO is the base-2 logarithm of the LZ77 window
         size, minus eight (CINFO=7 indicates a 32K window size). Values
         of CINFO above 7 are not allowed in this version of the
         specification.  CINFO is not defined in this specification for
         CM not equal to 8.

      FLG (FLaGs)
         This flag byte is divided as follows:

            bits 0 to 4  FCHECK  (check bits for CMF and FLG)
            bit  5       FDICT   (preset dictionary)
            bits 6 to 7  FLEVEL  (compression level)

         The FCHECK value must be such that CMF and FLG, when viewed as
         a 16-bit unsigned integer stored in MSB order (CMF*256 + FLG),
         is a multiple of 31.




Deutsch & Gailly             Informational                      [Page 5]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


      FDICT (Preset dictionary)
         If FDICT is set, a DICT dictionary identifier is present
         immediately after the FLG byte. The dictionary is a sequence of
         bytes which are initially fed to the compressor without
         producing any compressed output. DICT is the Adler-32 checksum
         of this sequence of bytes (see the definition of ADLER32
         below).  The decompressor can use this identifier to determine
         which dictionary has been used by the compressor.

      FLEVEL (Compression level)
         These flags are available for use by specific compression
         methods.  The "deflate" method (CM = 8) sets these flags as
         follows:

            0 - compressor used fastest algorithm
            1 - compressor used fast algorithm
            2 - compressor used default algorithm
            3 - compressor used maximum compression, slowest algorithm

         The information in FLEVEL is not needed for decompression; it
         is there to indicate if recompression might be worthwhile.

      compressed data
         For compression method 8, the compressed data is stored in the
         deflate compressed data format as described in the document
         "DEFLATE Compressed Data Format Specification" by L. Peter
         Deutsch. (See reference [3] in Chapter 3, below)

         Other compressed data formats are not specified in this version
         of the zlib specification.

      ADLER32 (Adler-32 checksum)
         This contains a checksum value of the uncompressed data
         (excluding any dictionary data) computed according to Adler-32
         algorithm. This algorithm is a 32-bit extension and improvement
         of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073
         standard. See references [4] and [5] in Chapter 3, below)

         Adler-32 is composed of two sums accumulated per byte: s1 is
         the sum of all bytes, s2 is the sum of all s1 values. Both sums
         are done modulo 65521. s1 is initialized to 1, s2 to zero.  The
         Adler-32 checksum is stored as s2*65536 + s1 in most-
         significant-byte first (network) order.








Deutsch & Gailly             Informational                      [Page 6]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


   2.3. Compliance

      A compliant compressor must produce streams with correct CMF, FLG
      and ADLER32, but need not support preset dictionaries.  When the
      zlib data format is used as part of another standard data format,
      the compressor may use only preset dictionaries that are specified
      by this other data format.  If this other format does not use the
      preset dictionary feature, the compressor must not set the FDICT
      flag.

      A compliant decompressor must check CMF, FLG, and ADLER32, and
      provide an error indication if any of these have incorrect values.
      A compliant decompressor must give an error indication if CM is
      not one of the values defined in this specification (only the
      value 8 is permitted in this version), since another value could
      indicate the presence of new features that would cause subsequent
      data to be interpreted incorrectly.  A compliant decompressor must
      give an error indication if FDICT is set and DICTID is not the
      identifier of a known preset dictionary.  A decompressor may
      ignore FLEVEL and still be compliant.  When the zlib data format
      is being used as a part of another standard format, a compliant
      decompressor must support all the preset dictionaries specified by
      the other format. When the other format does not use the preset
      dictionary feature, a compliant decompressor must reject any
      stream in which the FDICT flag is set.

3. References

   [1] Deutsch, L.P.,"GZIP Compressed Data Format Specification",
       available in ftp://ftp.uu.net/pub/archiving/zip/doc/

   [2] Thomas Boutell, "PNG (Portable Network Graphics) specification",
       available in ftp://ftp.uu.net/graphics/png/documents/

   [3] Deutsch, L.P.,"DEFLATE Compressed Data Format Specification",
       available in ftp://ftp.uu.net/pub/archiving/zip/doc/

   [4] Fletcher, J. G., "An Arithmetic Checksum for Serial
       Transmissions," IEEE Transactions on Communications, Vol. COM-30,
       No. 1, January 1982, pp. 247-252.

   [5] ITU-T Recommendation X.224, Annex D, "Checksum Algorithms,"
       November, 1993, pp. 144, 145. (Available from
       gopher://info.itu.ch). ITU-T X.244 is also the same as ISO 8073.







Deutsch & Gailly             Informational                      [Page 7]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


4. Source code

   Source code for a C language implementation of a "zlib" compliant
   library is available at ftp://ftp.uu.net/pub/archiving/zip/zlib/.

5. Security Considerations

   A decoder that fails to check the ADLER32 checksum value may be
   subject to undetected data corruption.

6. Acknowledgements

   Trademarks cited in this document are the property of their
   respective owners.

   Jean-Loup Gailly and Mark Adler designed the zlib format and wrote
   the related software described in this specification.  Glenn
   Randers-Pehrson converted this document to RFC and HTML format.

7. Authors' Addresses

   L. Peter Deutsch
   Aladdin Enterprises
   203 Santa Margarita Ave.
   Menlo Park, CA 94025

   Phone: (415) 322-0103 (AM only)
   FAX:   (415) 322-1734
   EMail: <ghost@aladdin.com>


   Jean-Loup Gailly

   EMail: <gzip@prep.ai.mit.edu>

   Questions about the technical content of this specification can be
   sent by email to

   Jean-Loup Gailly <gzip@prep.ai.mit.edu> and
   Mark Adler <madler@alumni.caltech.edu>

   Editorial comments on this specification can be sent by email to

   L. Peter Deutsch <ghost@aladdin.com> and
   Glenn Randers-Pehrson <randeg@alumni.rpi.edu>






Deutsch & Gailly             Informational                      [Page 8]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


8. Appendix: Rationale

   8.1. Preset dictionaries

      A preset dictionary is specially useful to compress short input
      sequences. The compressor can take advantage of the dictionary
      context to encode the input in a more compact manner. The
      decompressor can be initialized with the appropriate context by
      virtually decompressing a compressed version of the dictionary
      without producing any output. However for certain compression
      algorithms such as the deflate algorithm this operation can be
      achieved without actually performing any decompression.

      The compressor and the decompressor must use exactly the same
      dictionary. The dictionary may be fixed or may be chosen among a
      certain number of predefined dictionaries, according to the kind
      of input data. The decompressor can determine which dictionary has
      been chosen by the compressor by checking the dictionary
      identifier. This document does not specify the contents of
      predefined dictionaries, since the optimal dictionaries are
      application specific. Standard data formats using this feature of
      the zlib specification must precisely define the allowed
      dictionaries.

   8.2. The Adler-32 algorithm

      The Adler-32 algorithm is much faster than the CRC32 algorithm yet
      still provides an extremely low probability of undetected errors.

      The modulo on unsigned long accumulators can be delayed for 5552
      bytes, so the modulo operation time is negligible.  If the bytes
      are a, b, c, the second sum is 3a + 2b + c + 3, and so is position
      and order sensitive, unlike the first sum, which is just a
      checksum.  That 65521 is prime is important to avoid a possible
      large class of two-byte errors that leave the check unchanged.
      (The Fletcher checksum uses 255, which is not prime and which also
      makes the Fletcher check insensitive to single byte changes 0 <->
      255.)

      The sum s1 is initialized to 1 instead of zero to make the length
      of the sequence part of s2, so that the length does not have to be
      checked separately. (Any sequence of zeroes has a Fletcher
      checksum of zero.)








Deutsch & Gailly             Informational                      [Page 9]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


9. Appendix: Sample code

   The following C code computes the Adler-32 checksum of a data buffer.
   It is written for clarity, not for speed.  The sample code is in the
   ANSI C programming language. Non C users may find it easier to read
   with these hints:

      &      Bitwise AND operator.
      >>     Bitwise right shift operator. When applied to an
             unsigned quantity, as here, right shift inserts zero bit(s)
             at the left.
      <<     Bitwise left shift operator. Left shift inserts zero
             bit(s) at the right.
      ++     "n++" increments the variable n.
      %      modulo operator: a % b is the remainder of a divided by b.

      #define BASE 65521 /* largest prime smaller than 65536 */

      /*
         Update a running Adler-32 checksum with the bytes buf[0..len-1]
       and return the updated checksum. The Adler-32 checksum should be
       initialized to 1.

       Usage example:

         unsigned long adler = 1L;

         while (read_buffer(buffer, length) != EOF) {
           adler = update_adler32(adler, buffer, length);
         }
         if (adler != original_adler) error();
      */
      unsigned long update_adler32(unsigned long adler,
         unsigned char *buf, int len)
      {
        unsigned long s1 = adler & 0xffff;
        unsigned long s2 = (adler >> 16) & 0xffff;
        int n;

        for (n = 0; n < len; n++) {
          s1 = (s1 + buf[n]) % BASE;
          s2 = (s2 + s1)     % BASE;
        }
        return (s2 << 16) + s1;
      }

      /* Return the adler32 of the bytes buf[0..len-1] */




Deutsch & Gailly             Informational                     [Page 10]

RFC 1950       ZLIB Compressed Data Format Specification        May 1996


      unsigned long adler32(unsigned char *buf, int len)
      {
        return update_adler32(1L, buf, len);
      }















































Deutsch & Gailly             Informational                     [Page 11]


Network Working Group                                         P. Deutsch
Request for Comments: 1951                           Aladdin Enterprises
Category: Informational                                         May 1996


        DEFLATE Compressed Data Format Specification version 1.3

Status of This Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

IESG Note:

   The IESG takes no position on the validity of any Intellectual
   Property Rights statements contained in this document.

Notices

   Copyright (c) 1996 L. Peter Deutsch

   Permission is granted to copy and distribute this document for any
   purpose and without charge, including translations into other
   languages and incorporation into compilations, provided that the
   copyright notice and this notice are preserved, and that any
   substantive changes or deletions from the original are clearly
   marked.

   A pointer to the latest version of this and related documentation in
   HTML format can be found at the URL
   <ftp://ftp.uu.net/graphics/png/documents/zlib/zdoc-index.html>.

Abstract

   This specification defines a lossless compressed data format that
   compresses data using a combination of the LZ77 algorithm and Huffman
   coding, with efficiency comparable to the best currently available
   general-purpose compression methods.  The data can be produced or
   consumed, even for an arbitrarily long sequentially presented input
   data stream, using only an a priori bounded amount of intermediate
   storage.  The format can be implemented readily in a manner not
   covered by patents.








Deutsch                      Informational                      [Page 1]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


Table of Contents

   1. Introduction ................................................... 2
      1.1. Purpose ................................................... 2
      1.2. Intended audience ......................................... 3
      1.3. Scope ..................................................... 3
      1.4. Compliance ................................................ 3
      1.5.  Definitions of terms and conventions used ................ 3
      1.6. Changes from previous versions ............................ 4
   2. Compressed representation overview ............................. 4
   3. Detailed specification ......................................... 5
      3.1. Overall conventions ....................................... 5
          3.1.1. Packing into bytes .................................. 5
      3.2. Compressed block format ................................... 6
          3.2.1. Synopsis of prefix and Huffman coding ............... 6
          3.2.2. Use of Huffman coding in the "deflate" format ....... 7
          3.2.3. Details of block format ............................. 9
          3.2.4. Non-compressed blocks (BTYPE=00) ................... 11
          3.2.5. Compressed blocks (length and distance codes) ...... 11
          3.2.6. Compression with fixed Huffman codes (BTYPE=01) .... 12
          3.2.7. Compression with dynamic Huffman codes (BTYPE=10) .. 13
      3.3. Compliance ............................................... 14
   4. Compression algorithm details ................................. 14
   5. References .................................................... 16
   6. Security Considerations ....................................... 16
   7. Source code ................................................... 16
   8. Acknowledgements .............................................. 16
   9. Author's Address .............................................. 17

1. Introduction

   1.1. Purpose

      The purpose of this specification is to define a lossless
      compressed data format that:
          * Is independent of CPU type, operating system, file system,
            and character set, and hence can be used for interchange;
          * Can be produced or consumed, even for an arbitrarily long
            sequentially presented input data stream, using only an a
            priori bounded amount of intermediate storage, and hence
            can be used in data communications or similar structures
            such as Unix filters;
          * Compresses data with efficiency comparable to the best
            currently available general-purpose compression methods,
            and in particular considerably better than the "compress"
            program;
          * Can be implemented readily in a manner not covered by
            patents, and hence can be practiced freely;



Deutsch                      Informational                      [Page 2]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


          * Is compatible with the file format produced by the current
            widely used gzip utility, in that conforming decompressors
            will be able to read data produced by the existing gzip
            compressor.

      The data format defined by this specification does not attempt to:

          * Allow random access to compressed data;
          * Compress specialized data (e.g., raster graphics) as well
            as the best currently available specialized algorithms.

      A simple counting argument shows that no lossless compression
      algorithm can compress every possible input data set.  For the
      format defined here, the worst case expansion is 5 bytes per 32K-
      byte block, i.e., a size increase of 0.015% for large data sets.
      English text usually compresses by a factor of 2.5 to 3;
      executable files usually compress somewhat less; graphical data
      such as raster images may compress much more.

   1.2. Intended audience

      This specification is intended for use by implementors of software
      to compress data into "deflate" format and/or decompress data from
      "deflate" format.

      The text of the specification assumes a basic background in
      programming at the level of bits and other primitive data
      representations.  Familiarity with the technique of Huffman coding
      is helpful but not required.

   1.3. Scope

      The specification specifies a method for representing a sequence
      of bytes as a (usually shorter) sequence of bits, and a method for
      packing the latter bit sequence into bytes.

   1.4. Compliance

      Unless otherwise indicated below, a compliant decompressor must be
      able to accept and decompress any data set that conforms to all
      the specifications presented here; a compliant compressor must
      produce data sets that conform to all the specifications presented
      here.

   1.5.  Definitions of terms and conventions used

      Byte: 8 bits stored or transmitted as a unit (same as an octet).
      For this specification, a byte is exactly 8 bits, even on machines



Deutsch                      Informational                      [Page 3]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


      which store a character on a number of bits different from eight.
      See below, for the numbering of bits within a byte.

      String: a sequence of arbitrary bytes.

   1.6. Changes from previous versions

      There have been no technical changes to the deflate format since
      version 1.1 of this specification.  In version 1.2, some
      terminology was changed.  Version 1.3 is a conversion of the
      specification to RFC style.

2. Compressed representation overview

   A compressed data set consists of a series of blocks, corresponding
   to successive blocks of input data.  The block sizes are arbitrary,
   except that non-compressible blocks are limited to 65,535 bytes.

   Each block is compressed using a combination of the LZ77 algorithm
   and Huffman coding. The Huffman trees for each block are independent
   of those for previous or subsequent blocks; the LZ77 algorithm may
   use a reference to a duplicated string occurring in a previous block,
   up to 32K input bytes before.

   Each block consists of two parts: a pair of Huffman code trees that
   describe the representation of the compressed data part, and a
   compressed data part.  (The Huffman trees themselves are compressed
   using Huffman encoding.)  The compressed data consists of a series of
   elements of two types: literal bytes (of strings that have not been
   detected as duplicated within the previous 32K input bytes), and
   pointers to duplicated strings, where a pointer is represented as a
   pair <length, backward distance>.  The representation used in the
   "deflate" format limits distances to 32K bytes and lengths to 258
   bytes, but does not limit the size of a block, except for
   uncompressible blocks, which are limited as noted above.

   Each type of value (literals, distances, and lengths) in the
   compressed data is represented using a Huffman code, using one code
   tree for literals and lengths and a separate code tree for distances.
   The code trees for each block appear in a compact form just before
   the compressed data for that block.










Deutsch                      Informational                      [Page 4]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


3. Detailed specification

   3.1. Overall conventions In the diagrams below, a box like this:

         +---+
         |   | <-- the vertical bars might be missing
         +---+

      represents one byte; a box like this:

         +==============+
         |              |
         +==============+

      represents a variable number of bytes.

      Bytes stored within a computer do not have a "bit order", since
      they are always treated as a unit.  However, a byte considered as
      an integer between 0 and 255 does have a most- and least-
      significant bit, and since we write numbers with the most-
      significant digit on the left, we also write bytes with the most-
      significant bit on the left.  In the diagrams below, we number the
      bits of a byte so that bit 0 is the least-significant bit, i.e.,
      the bits are numbered:

         +--------+
         |76543210|
         +--------+

      Within a computer, a number may occupy multiple bytes.  All
      multi-byte numbers in the format described here are stored with
      the least-significant byte first (at the lower memory address).
      For example, the decimal number 520 is stored as:

             0        1
         +--------+--------+
         |00001000|00000010|
         +--------+--------+
          ^        ^
          |        |
          |        + more significant byte = 2 x 256
          + less significant byte = 8

      3.1.1. Packing into bytes

         This document does not address the issue of the order in which
         bits of a byte are transmitted on a bit-sequential medium,
         since the final data format described here is byte- rather than



Deutsch                      Informational                      [Page 5]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


         bit-oriented.  However, we describe the compressed block format
         in below, as a sequence of data elements of various bit
         lengths, not a sequence of bytes.  We must therefore specify
         how to pack these data elements into bytes to form the final
         compressed byte sequence:

             * Data elements are packed into bytes in order of
               increasing bit number within the byte, i.e., starting
               with the least-significant bit of the byte.
             * Data elements other than Huffman codes are packed
               starting with the least-significant bit of the data
               element.
             * Huffman codes are packed starting with the most-
               significant bit of the code.

         In other words, if one were to print out the compressed data as
         a sequence of bytes, starting with the first byte at the
         *right* margin and proceeding to the *left*, with the most-
         significant bit of each byte on the left as usual, one would be
         able to parse the result from right to left, with fixed-width
         elements in the correct MSB-to-LSB order and Huffman codes in
         bit-reversed order (i.e., with the first bit of the code in the
         relative LSB position).

   3.2. Compressed block format

      3.2.1. Synopsis of prefix and Huffman coding

         Prefix coding represents symbols from an a priori known
         alphabet by bit sequences (codes), one code for each symbol, in
         a manner such that different symbols may be represented by bit
         sequences of different lengths, but a parser can always parse
         an encoded string unambiguously symbol-by-symbol.

         We define a prefix code in terms of a binary tree in which the
         two edges descending from each non-leaf node are labeled 0 and
         1 and in which the leaf nodes correspond one-for-one with (are
         labeled with) the symbols of the alphabet; then the code for a
         symbol is the sequence of 0's and 1's on the edges leading from
         the root to the leaf labeled with that symbol.  For example:











Deutsch                      Informational                      [Page 6]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


                          /\              Symbol    Code
                         0  1             ------    ----
                        /    \                A      00
                       /\     B               B       1
                      0  1                    C     011
                     /    \                   D     010
                    A     /\
                         0  1
                        /    \
                       D      C

         A parser can decode the next symbol from an encoded input
         stream by walking down the tree from the root, at each step
         choosing the edge corresponding to the next input bit.

         Given an alphabet with known symbol frequencies, the Huffman
         algorithm allows the construction of an optimal prefix code
         (one which represents strings with those symbol frequencies
         using the fewest bits of any possible prefix codes for that
         alphabet).  Such a code is called a Huffman code.  (See
         reference [1] in Chapter 5, references for additional
         information on Huffman codes.)

         Note that in the "deflate" format, the Huffman codes for the
         various alphabets must not exceed certain maximum code lengths.
         This constraint complicates the algorithm for computing code
         lengths from symbol frequencies.  Again, see Chapter 5,
         references for details.

      3.2.2. Use of Huffman coding in the "deflate" format

         The Huffman codes used for each alphabet in the "deflate"
         format have two additional rules:

             * All codes of a given bit length have lexicographically
               consecutive values, in the same order as the symbols
               they represent;

             * Shorter codes lexicographically precede longer codes.












Deutsch                      Informational                      [Page 7]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


         We could recode the example above to follow this rule as
         follows, assuming that the order of the alphabet is ABCD:

            Symbol  Code
            ------  ----
            A       10
            B       0
            C       110
            D       111

         I.e., 0 precedes 10 which precedes 11x, and 110 and 111 are
         lexicographically consecutive.

         Given this rule, we can define the Huffman code for an alphabet
         just by giving the bit lengths of the codes for each symbol of
         the alphabet in order; this is sufficient to determine the
         actual codes.  In our example, the code is completely defined
         by the sequence of bit lengths (2, 1, 3, 3).  The following
         algorithm generates the codes as integers, intended to be read
         from most- to least-significant bit.  The code lengths are
         initially in tree[I].Len; the codes are produced in
         tree[I].Code.

         1)  Count the number of codes for each code length.  Let
             bl_count[N] be the number of codes of length N, N >= 1.

         2)  Find the numerical value of the smallest code for each
             code length:

                code = 0;
                bl_count[0] = 0;
                for (bits = 1; bits <= MAX_BITS; bits++) {
                    code = (code + bl_count[bits-1]) << 1;
                    next_code[bits] = code;
                }

         3)  Assign numerical values to all codes, using consecutive
             values for all codes of the same length with the base
             values determined at step 2. Codes that are never used
             (which have a bit length of zero) must not be assigned a
             value.

                for (n = 0;  n <= max_code; n++) {
                    len = tree[n].Len;
                    if (len != 0) {
                        tree[n].Code = next_code[len];
                        next_code[len]++;
                    }



Deutsch                      Informational                      [Page 8]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


                }

         Example:

         Consider the alphabet ABCDEFGH, with bit lengths (3, 3, 3, 3,
         3, 2, 4, 4).  After step 1, we have:

            N      bl_count[N]
            -      -----------
            2      1
            3      5
            4      2

         Step 2 computes the following next_code values:

            N      next_code[N]
            -      ------------
            1      0
            2      0
            3      2
            4      14

         Step 3 produces the following code values:

            Symbol Length   Code
            ------ ------   ----
            A       3        010
            B       3        011
            C       3        100
            D       3        101
            E       3        110
            F       2         00
            G       4       1110
            H       4       1111

      3.2.3. Details of block format

         Each block of compressed data begins with 3 header bits
         containing the following data:

            first bit       BFINAL
            next 2 bits     BTYPE

         Note that the header bits do not necessarily begin on a byte
         boundary, since a block does not necessarily occupy an integral
         number of bytes.





Deutsch                      Informational                      [Page 9]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


         BFINAL is set if and only if this is the last block of the data
         set.

         BTYPE specifies how the data are compressed, as follows:

            00 - no compression
            01 - compressed with fixed Huffman codes
            10 - compressed with dynamic Huffman codes
            11 - reserved (error)

         The only difference between the two compressed cases is how the
         Huffman codes for the literal/length and distance alphabets are
         defined.

         In all cases, the decoding algorithm for the actual data is as
         follows:

            do
               read block header from input stream.
               if stored with no compression
                  skip any remaining bits in current partially
                     processed byte
                  read LEN and NLEN (see next section)
                  copy LEN bytes of data to output
               otherwise
                  if compressed with dynamic Huffman codes
                     read representation of code trees (see
                        subsection below)
                  loop (until end of block code recognized)
                     decode literal/length value from input stream
                     if value < 256
                        copy value (literal byte) to output stream
                     otherwise
                        if value = end of block (256)
                           break from loop
                        otherwise (value = 257..285)
                           decode distance from input stream

                           move backwards distance bytes in the output
                           stream, and copy length bytes from this
                           position to the output stream.
                  end loop
            while not last block

         Note that a duplicated string reference may refer to a string
         in a previous block; i.e., the backward distance may cross one
         or more block boundaries.  However a distance cannot refer past
         the beginning of the output stream.  (An application using a



Deutsch                      Informational                     [Page 10]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


         preset dictionary might discard part of the output stream; a
         distance can refer to that part of the output stream anyway)
         Note also that the referenced string may overlap the current
         position; for example, if the last 2 bytes decoded have values
         X and Y, a string reference with <length = 5, distance = 2>
         adds X,Y,X,Y,X to the output stream.

         We now specify each compression method in turn.

      3.2.4. Non-compressed blocks (BTYPE=00)

         Any bits of input up to the next byte boundary are ignored.
         The rest of the block consists of the following information:

              0   1   2   3   4...
            +---+---+---+---+================================+
            |  LEN  | NLEN  |... LEN bytes of literal data...|
            +---+---+---+---+================================+

         LEN is the number of data bytes in the block.  NLEN is the
         one's complement of LEN.

      3.2.5. Compressed blocks (length and distance codes)

         As noted above, encoded data blocks in the "deflate" format
         consist of sequences of symbols drawn from three conceptually
         distinct alphabets: either literal bytes, from the alphabet of
         byte values (0..255), or <length, backward distance> pairs,
         where the length is drawn from (3..258) and the distance is
         drawn from (1..32,768).  In fact, the literal and length
         alphabets are merged into a single alphabet (0..285), where
         values 0..255 represent literal bytes, the value 256 indicates
         end-of-block, and values 257..285 represent length codes
         (possibly in conjunction with extra bits following the symbol
         code) as follows:
















Deutsch                      Informational                     [Page 11]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


                 Extra               Extra               Extra
            Code Bits Length(s) Code Bits Lengths   Code Bits Length(s)
            ---- ---- ------     ---- ---- -------   ---- ---- -------
             257   0     3       267   1   15,16     277   4   67-82
             258   0     4       268   1   17,18     278   4   83-98
             259   0     5       269   2   19-22     279   4   99-114
             260   0     6       270   2   23-26     280   4  115-130
             261   0     7       271   2   27-30     281   5  131-162
             262   0     8       272   2   31-34     282   5  163-194
             263   0     9       273   3   35-42     283   5  195-226
             264   0    10       274   3   43-50     284   5  227-257
             265   1  11,12      275   3   51-58     285   0    258
             266   1  13,14      276   3   59-66

         The extra bits should be interpreted as a machine integer
         stored with the most-significant bit first, e.g., bits 1110
         represent the value 14.

                  Extra           Extra               Extra
             Code Bits Dist  Code Bits   Dist     Code Bits Distance
             ---- ---- ----  ---- ----  ------    ---- ---- --------
               0   0    1     10   4     33-48    20    9   1025-1536
               1   0    2     11   4     49-64    21    9   1537-2048
               2   0    3     12   5     65-96    22   10   2049-3072
               3   0    4     13   5     97-128   23   10   3073-4096
               4   1   5,6    14   6    129-192   24   11   4097-6144
               5   1   7,8    15   6    193-256   25   11   6145-8192
               6   2   9-12   16   7    257-384   26   12  8193-12288
               7   2  13-16   17   7    385-512   27   12 12289-16384
               8   3  17-24   18   8    513-768   28   13 16385-24576
               9   3  25-32   19   8   769-1024   29   13 24577-32768

      3.2.6. Compression with fixed Huffman codes (BTYPE=01)

         The Huffman codes for the two alphabets are fixed, and are not
         represented explicitly in the data.  The Huffman code lengths
         for the literal/length alphabet are:

                   Lit Value    Bits        Codes
                   ---------    ----        -----
                     0 - 143     8          00110000 through
                                            10111111
                   144 - 255     9          110010000 through
                                            111111111
                   256 - 279     7          0000000 through
                                            0010111
                   280 - 287     8          11000000 through
                                            11000111



Deutsch                      Informational                     [Page 12]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


         The code lengths are sufficient to generate the actual codes,
         as described above; we show the codes in the table for added
         clarity.  Literal/length values 286-287 will never actually
         occur in the compressed data, but participate in the code
         construction.

         Distance codes 0-31 are represented by (fixed-length) 5-bit
         codes, with possible additional bits as shown in the table
         shown in Paragraph 3.2.5, above.  Note that distance codes 30-
         31 will never actually occur in the compressed data.

      3.2.7. Compression with dynamic Huffman codes (BTYPE=10)

         The Huffman codes for the two alphabets appear in the block
         immediately after the header bits and before the actual
         compressed data, first the literal/length code and then the
         distance code.  Each code is defined by a sequence of code
         lengths, as discussed in Paragraph 3.2.2, above.  For even
         greater compactness, the code length sequences themselves are
         compressed using a Huffman code.  The alphabet for code lengths
         is as follows:

               0 - 15: Represent code lengths of 0 - 15
                   16: Copy the previous code length 3 - 6 times.
                       The next 2 bits indicate repeat length
                             (0 = 3, ... , 3 = 6)
                          Example:  Codes 8, 16 (+2 bits 11),
                                    16 (+2 bits 10) will expand to
                                    12 code lengths of 8 (1 + 6 + 5)
                   17: Repeat a code length of 0 for 3 - 10 times.
                       (3 bits of length)
                   18: Repeat a code length of 0 for 11 - 138 times
                       (7 bits of length)

         A code length of 0 indicates that the corresponding symbol in
         the literal/length or distance alphabet will not occur in the
         block, and should not participate in the Huffman code
         construction algorithm given earlier.  If only one distance
         code is used, it is encoded using one bit, not zero bits; in
         this case there is a single code length of one, with one unused
         code.  One distance code of zero bits means that there are no
         distance codes used at all (the data is all literals).

         We can now define the format of the block:

               5 Bits: HLIT, # of Literal/Length codes - 257 (257 - 286)
               5 Bits: HDIST, # of Distance codes - 1        (1 - 32)
               4 Bits: HCLEN, # of Code Length codes - 4     (4 - 19)



Deutsch                      Informational                     [Page 13]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


               (HCLEN + 4) x 3 bits: code lengths for the code length
                  alphabet given just above, in the order: 16, 17, 18,
                  0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15

                  These code lengths are interpreted as 3-bit integers
                  (0-7); as above, a code length of 0 means the
                  corresponding symbol (literal/length or distance code
                  length) is not used.

               HLIT + 257 code lengths for the literal/length alphabet,
                  encoded using the code length Huffman code

               HDIST + 1 code lengths for the distance alphabet,
                  encoded using the code length Huffman code

               The actual compressed data of the block,
                  encoded using the literal/length and distance Huffman
                  codes

               The literal/length symbol 256 (end of data),
                  encoded using the literal/length Huffman code

         The code length repeat codes can cross from HLIT + 257 to the
         HDIST + 1 code lengths.  In other words, all code lengths form
         a single sequence of HLIT + HDIST + 258 values.

   3.3. Compliance

      A compressor may limit further the ranges of values specified in
      the previous section and still be compliant; for example, it may
      limit the range of backward pointers to some value smaller than
      32K.  Similarly, a compressor may limit the size of blocks so that
      a compressible block fits in memory.

      A compliant decompressor must accept the full range of possible
      values defined in the previous section, and must accept blocks of
      arbitrary size.

4. Compression algorithm details

   While it is the intent of this document to define the "deflate"
   compressed data format without reference to any particular
   compression algorithm, the format is related to the compressed
   formats produced by LZ77 (Lempel-Ziv 1977, see reference [2] below);
   since many variations of LZ77 are patented, it is strongly
   recommended that the implementor of a compressor follow the general
   algorithm presented here, which is known not to be patented per se.
   The material in this section is not part of the definition of the



Deutsch                      Informational                     [Page 14]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


   specification per se, and a compressor need not follow it in order to
   be compliant.

   The compressor terminates a block when it determines that starting a
   new block with fresh trees would be useful, or when the block size
   fills up the compressor's block buffer.

   The compressor uses a chained hash table to find duplicated strings,
   using a hash function that operates on 3-byte sequences.  At any
   given point during compression, let XYZ be the next 3 input bytes to
   be examined (not necessarily all different, of course).  First, the
   compressor examines the hash chain for XYZ.  If the chain is empty,
   the compressor simply writes out X as a literal byte and advances one
   byte in the input.  If the hash chain is not empty, indicating that
   the sequence XYZ (or, if we are unlucky, some other 3 bytes with the
   same hash function value) has occurred recently, the compressor
   compares all strings on the XYZ hash chain with the actual input data
   sequence starting at the current point, and selects the longest
   match.

   The compressor searches the hash chains starting with the most recent
   strings, to favor small distances and thus take advantage of the
   Huffman encoding.  The hash chains are singly linked. There are no
   deletions from the hash chains; the algorithm simply discards matches
   that are too old.  To avoid a worst-case situation, very long hash
   chains are arbitrarily truncated at a certain length, determined by a
   run-time parameter.

   To improve overall compression, the compressor optionally defers the
   selection of matches ("lazy matching"): after a match of length N has
   been found, the compressor searches for a longer match starting at
   the next input byte.  If it finds a longer match, it truncates the
   previous match to a length of one (thus producing a single literal
   byte) and then emits the longer match.  Otherwise, it emits the
   original match, and, as described above, advances N bytes before
   continuing.

   Run-time parameters also control this "lazy match" procedure.  If
   compression ratio is most important, the compressor attempts a
   complete second search regardless of the length of the first match.
   In the normal case, if the current match is "long enough", the
   compressor reduces the search for a longer match, thus speeding up
   the process.  If speed is most important, the compressor inserts new
   strings in the hash table only when no match was found, or when the
   match is not "too long".  This degrades the compression ratio but
   saves time since there are both fewer insertions and fewer searches.





Deutsch                      Informational                     [Page 15]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


5. References

   [1] Huffman, D. A., "A Method for the Construction of Minimum
       Redundancy Codes", Proceedings of the Institute of Radio
       Engineers, September 1952, Volume 40, Number 9, pp. 1098-1101.

   [2] Ziv J., Lempel A., "A Universal Algorithm for Sequential Data
       Compression", IEEE Transactions on Information Theory, Vol. 23,
       No. 3, pp. 337-343.

   [3] Gailly, J.-L., and Adler, M., ZLIB documentation and sources,
       available in ftp://ftp.uu.net/pub/archiving/zip/doc/

   [4] Gailly, J.-L., and Adler, M., GZIP documentation and sources,
       available as gzip-*.tar in ftp://prep.ai.mit.edu/pub/gnu/

   [5] Schwartz, E. S., and Kallick, B. "Generating a canonical prefix
       encoding." Comm. ACM, 7,3 (Mar. 1964), pp. 166-169.

   [6] Hirschberg and Lelewer, "Efficient decoding of prefix codes,"
       Comm. ACM, 33,4, April 1990, pp. 449-459.

6. Security Considerations

   Any data compression method involves the reduction of redundancy in
   the data.  Consequently, any corruption of the data is likely to have
   severe effects and be difficult to correct.  Uncompressed text, on
   the other hand, will probably still be readable despite the presence
   of some corrupted bytes.

   It is recommended that systems using this data format provide some
   means of validating the integrity of the compressed data.  See
   reference [3], for example.

7. Source code

   Source code for a C language implementation of a "deflate" compliant
   compressor and decompressor is available within the zlib package at
   ftp://ftp.uu.net/pub/archiving/zip/zlib/.

8. Acknowledgements

   Trademarks cited in this document are the property of their
   respective owners.

   Phil Katz designed the deflate format.  Jean-Loup Gailly and Mark
   Adler wrote the related software described in this specification.
   Glenn Randers-Pehrson converted this document to RFC and HTML format.



Deutsch                      Informational                     [Page 16]

RFC 1951      DEFLATE Compressed Data Format Specification      May 1996


9. Author's Address

   L. Peter Deutsch
   Aladdin Enterprises
   203 Santa Margarita Ave.
   Menlo Park, CA 94025

   Phone: (415) 322-0103 (AM only)
   FAX:   (415) 322-1734
   EMail: <ghost@aladdin.com>

   Questions about the technical content of this specification can be
   sent by email to:

   Jean-Loup Gailly <gzip@prep.ai.mit.edu> and
   Mark Adler <madler@alumni.caltech.edu>

   Editorial comments on this specification can be sent by email to:

   L. Peter Deutsch <ghost@aladdin.com> and
   Glenn Randers-Pehrson <randeg@alumni.rpi.edu>






























Deutsch                      Informational                     [Page 17]


Network Working Group                                         P. Deutsch
Request for Comments: 1952                           Aladdin Enterprises
Category: Informational                                         May 1996


               GZIP file format specification version 4.3

Status of This Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

IESG Note:

   The IESG takes no position on the validity of any Intellectual
   Property Rights statements contained in this document.

Notices

   Copyright (c) 1996 L. Peter Deutsch

   Permission is granted to copy and distribute this document for any
   purpose and without charge, including translations into other
   languages and incorporation into compilations, provided that the
   copyright notice and this notice are preserved, and that any
   substantive changes or deletions from the original are clearly
   marked.

   A pointer to the latest version of this and related documentation in
   HTML format can be found at the URL
   <ftp://ftp.uu.net/graphics/png/documents/zlib/zdoc-index.html>.

Abstract

   This specification defines a lossless compressed data format that is
   compatible with the widely used GZIP utility.  The format includes a
   cyclic redundancy check value for detecting data corruption.  The
   format presently uses the DEFLATE method of compression but can be
   easily extended to use other compression methods.  The format can be
   implemented readily in a manner not covered by patents.










Deutsch                      Informational                      [Page 1]

RFC 1952             GZIP File Format Specification             May 1996


Table of Contents

   1. Introduction ................................................... 2
      1.1. Purpose ................................................... 2
      1.2. Intended audience ......................................... 3
      1.3. Scope ..................................................... 3
      1.4. Compliance ................................................ 3
      1.5. Definitions of terms and conventions used ................. 3
      1.6. Changes from previous versions ............................ 3
   2. Detailed specification ......................................... 4
      2.1. Overall conventions ....................................... 4
      2.2. File format ............................................... 5
      2.3. Member format ............................................. 5
          2.3.1. Member header and trailer ........................... 6
              2.3.1.1. Extra field ................................... 8
              2.3.1.2. Compliance .................................... 9
      3. References .................................................. 9
      4. Security Considerations .................................... 10
      5. Acknowledgements ........................................... 10
      6. Author's Address ........................................... 10
      7. Appendix: Jean-Loup Gailly's gzip utility .................. 11
      8. Appendix: Sample CRC Code .................................. 11

1. Introduction

   1.1. Purpose

      The purpose of this specification is to define a lossless
      compressed data format that:

          * Is independent of CPU type, operating system, file system,
            and character set, and hence can be used for interchange;
          * Can compress or decompress a data stream (as opposed to a
            randomly accessible file) to produce another data stream,
            using only an a priori bounded amount of intermediate
            storage, and hence can be used in data communications or
            similar structures such as Unix filters;
          * Compresses data with efficiency comparable to the best
            currently available general-purpose compression methods,
            and in particular considerably better than the "compress"
            program;
          * Can be implemented readily in a manner not covered by
            patents, and hence can be practiced freely;
          * Is compatible with the file format produced by the current
            widely used gzip utility, in that conforming decompressors
            will be able to read data produced by the existing gzip
            compressor.




Deutsch                      Informational                      [Page 2]

RFC 1952             GZIP File Format Specification             May 1996


      The data format defined by this specification does not attempt to:

          * Provide random access to compressed data;
          * Compress specialized data (e.g., raster graphics) as well as
            the best currently available specialized algorithms.

   1.2. Intended audience

      This specification is intended for use by implementors of software
      to compress data into gzip format and/or decompress data from gzip
      format.

      The text of the specification assumes a basic background in
      programming at the level of bits and other primitive data
      representations.

   1.3. Scope

      The specification specifies a compression method and a file format
      (the latter assuming only that a file can store a sequence of
      arbitrary bytes).  It does not specify any particular interface to
      a file system or anything about character sets or encodings
      (except for file names and comments, which are optional).

   1.4. Compliance

      Unless otherwise indicated below, a compliant decompressor must be
      able to accept and decompress any file that conforms to all the
      specifications presented here; a compliant compressor must produce
      files that conform to all the specifications presented here.  The
      material in the appendices is not part of the specification per se
      and is not relevant to compliance.

   1.5. Definitions of terms and conventions used

      byte: 8 bits stored or transmitted as a unit (same as an octet).
      (For this specification, a byte is exactly 8 bits, even on
      machines which store a character on a number of bits different
      from 8.)  See below for the numbering of bits within a byte.

   1.6. Changes from previous versions

      There have been no technical changes to the gzip format since
      version 4.1 of this specification.  In version 4.2, some
      terminology was changed, and the sample CRC code was rewritten for
      clarity and to eliminate the requirement for the caller to do pre-
      and post-conditioning.  Version 4.3 is a conversion of the
      specification to RFC style.



Deutsch                      Informational                      [Page 3]

RFC 1952             GZIP File Format Specification             May 1996


2. Detailed specification

   2.1. Overall conventions

      In the diagrams below, a box like this:

         +---+
         |   | <-- the vertical bars might be missing
         +---+

      represents one byte; a box like this:

         +==============+
         |              |
         +==============+

      represents a variable number of bytes.

      Bytes stored within a computer do not have a "bit order", since
      they are always treated as a unit.  However, a byte considered as
      an integer between 0 and 255 does have a most- and least-
      significant bit, and since we write numbers with the most-
      significant digit on the left, we also write bytes with the most-
      significant bit on the left.  In the diagrams below, we number the
      bits of a byte so that bit 0 is the least-significant bit, i.e.,
      the bits are numbered:

         +--------+
         |76543210|
         +--------+

      This document does not address the issue of the order in which
      bits of a byte are transmitted on a bit-sequential medium, since
      the data format described here is byte- rather than bit-oriented.

      Within a computer, a number may occupy multiple bytes.  All
      multi-byte numbers in the format described here are stored with
      the least-significant byte first (at the lower memory address).
      For example, the decimal number 520 is stored as:

             0        1
         +--------+--------+
         |00001000|00000010|
         +--------+--------+
          ^        ^
          |        |
          |        + more significant byte = 2 x 256
          + less significant byte = 8



Deutsch                      Informational                      [Page 4]

RFC 1952             GZIP File Format Specification             May 1996


   2.2. File format

      A gzip file consists of a series of "members" (compressed data
      sets).  The format of each member is specified in the following
      section.  The members simply appear one after another in the file,
      with no additional information before, between, or after them.

   2.3. Member format

      Each member has the following structure:

         +---+---+---+---+---+---+---+---+---+---+
         |ID1|ID2|CM |FLG|     MTIME     |XFL|OS | (more-->)
         +---+---+---+---+---+---+---+---+---+---+

      (if FLG.FEXTRA set)

         +---+---+=================================+
         | XLEN  |...XLEN bytes of "extra field"...| (more-->)
         +---+---+=================================+

      (if FLG.FNAME set)

         +=========================================+
         |...original file name, zero-terminated...| (more-->)
         +=========================================+

      (if FLG.FCOMMENT set)

         +===================================+
         |...file comment, zero-terminated...| (more-->)
         +===================================+

      (if FLG.FHCRC set)

         +---+---+
         | CRC16 |
         +---+---+

         +=======================+
         |...compressed blocks...| (more-->)
         +=======================+

           0   1   2   3   4   5   6   7
         +---+---+---+---+---+---+---+---+
         |     CRC32     |     ISIZE     |
         +---+---+---+---+---+---+---+---+




Deutsch                      Informational                      [Page 5]

RFC 1952             GZIP File Format Specification             May 1996


      2.3.1. Member header and trailer

         ID1 (IDentification 1)
         ID2 (IDentification 2)
            These have the fixed values ID1 = 31 (0x1f, \037), ID2 = 139
            (0x8b, \213), to identify the file as being in gzip format.

         CM (Compression Method)
            This identifies the compression method used in the file.  CM
            = 0-7 are reserved.  CM = 8 denotes the "deflate"
            compression method, which is the one customarily used by
            gzip and which is documented elsewhere.

         FLG (FLaGs)
            This flag byte is divided into individual bits as follows:

               bit 0   FTEXT
               bit 1   FHCRC
               bit 2   FEXTRA
               bit 3   FNAME
               bit 4   FCOMMENT
               bit 5   reserved
               bit 6   reserved
               bit 7   reserved

            If FTEXT is set, the file is probably ASCII text.  This is
            an optional indication, which the compressor may set by
            checking a small amount of the input data to see whether any
            non-ASCII characters are present.  In case of doubt, FTEXT
            is cleared, indicating binary data. For systems which have
            different file formats for ascii text and binary data, the
            decompressor can use FTEXT to choose the appropriate format.
            We deliberately do not specify the algorithm used to set
            this bit, since a compressor always has the option of
            leaving it cleared and a decompressor always has the option
            of ignoring it and letting some other program handle issues
            of data conversion.

            If FHCRC is set, a CRC16 for the gzip header is present,
            immediately before the compressed data. The CRC16 consists
            of the two least significant bytes of the CRC32 for all
            bytes of the gzip header up to and not including the CRC16.
            [The FHCRC bit was never set by versions of gzip up to
            1.2.4, even though it was documented with a different
            meaning in gzip 1.2.4.]

            If FEXTRA is set, optional extra fields are present, as
            described in a following section.



Deutsch                      Informational                      [Page 6]

RFC 1952             GZIP File Format Specification             May 1996


            If FNAME is set, an original file name is present,
            terminated by a zero byte.  The name must consist of ISO
            8859-1 (LATIN-1) characters; on operating systems using
            EBCDIC or any other character set for file names, the name
            must be translated to the ISO LATIN-1 character set.  This
            is the original name of the file being compressed, with any
            directory components removed, and, if the file being
            compressed is on a file system with case insensitive names,
            forced to lower case. There is no original file name if the
            data was compressed from a source other than a named file;
            for example, if the source was stdin on a Unix system, there
            is no file name.

            If FCOMMENT is set, a zero-terminated file comment is
            present.  This comment is not interpreted; it is only
            intended for human consumption.  The comment must consist of
            ISO 8859-1 (LATIN-1) characters.  Line breaks should be
            denoted by a single line feed character (10 decimal).

            Reserved FLG bits must be zero.

         MTIME (Modification TIME)
            This gives the most recent modification time of the original
            file being compressed.  The time is in Unix format, i.e.,
            seconds since 00:00:00 GMT, Jan.  1, 1970.  (Note that this
            may cause problems for MS-DOS and other systems that use
            local rather than Universal time.)  If the compressed data
            did not come from a file, MTIME is set to the time at which
            compression started.  MTIME = 0 means no time stamp is
            available.

         XFL (eXtra FLags)
            These flags are available for use by specific compression
            methods.  The "deflate" method (CM = 8) sets these flags as
            follows:

               XFL = 2 - compressor used maximum compression,
                         slowest algorithm
               XFL = 4 - compressor used fastest algorithm

         OS (Operating System)
            This identifies the type of file system on which compression
            took place.  This may be useful in determining end-of-line
            convention for text files.  The currently defined values are
            as follows:






Deutsch                      Informational                      [Page 7]

RFC 1952             GZIP File Format Specification             May 1996


                 0 - FAT filesystem (MS-DOS, OS/2, NT/Win32)
                 1 - Amiga
                 2 - VMS (or OpenVMS)
                 3 - Unix
                 4 - VM/CMS
                 5 - Atari TOS
                 6 - HPFS filesystem (OS/2, NT)
                 7 - Macintosh
                 8 - Z-System
                 9 - CP/M
                10 - TOPS-20
                11 - NTFS filesystem (NT)
                12 - QDOS
                13 - Acorn RISCOS
               255 - unknown

         XLEN (eXtra LENgth)
            If FLG.FEXTRA is set, this gives the length of the optional
            extra field.  See below for details.

         CRC32 (CRC-32)
            This contains a Cyclic Redundancy Check value of the
            uncompressed data computed according to CRC-32 algorithm
            used in the ISO 3309 standard and in section 8.1.1.6.2 of
            ITU-T recommendation V.42.  (See http://www.iso.ch for
            ordering ISO documents. See gopher://info.itu.ch for an
            online version of ITU-T V.42.)

         ISIZE (Input SIZE)
            This contains the size of the original (uncompressed) input
            data modulo 2^32.

      2.3.1.1. Extra field

         If the FLG.FEXTRA bit is set, an "extra field" is present in
         the header, with total length XLEN bytes.  It consists of a
         series of subfields, each of the form:

            +---+---+---+---+==================================+
            |SI1|SI2|  LEN  |... LEN bytes of subfield data ...|
            +---+---+---+---+==================================+

         SI1 and SI2 provide a subfield ID, typically two ASCII letters
         with some mnemonic value.  Jean-Loup Gailly
         <gzip@prep.ai.mit.edu> is maintaining a registry of subfield
         IDs; please send him any subfield ID you wish to use.  Subfield
         IDs with SI2 = 0 are reserved for future use.  The following
         IDs are currently defined:



Deutsch                      Informational                      [Page 8]

RFC 1952             GZIP File Format Specification             May 1996


            SI1         SI2         Data
            ----------  ----------  ----
            0x41 ('A')  0x70 ('P')  Apollo file type information

         LEN gives the length of the subfield data, excluding the 4
         initial bytes.

      2.3.1.2. Compliance

         A compliant compressor must produce files with correct ID1,
         ID2, CM, CRC32, and ISIZE, but may set all the other fields in
         the fixed-length part of the header to default values (255 for
         OS, 0 for all others).  The compressor must set all reserved
         bits to zero.

         A compliant decompressor must check ID1, ID2, and CM, and
         provide an error indication if any of these have incorrect
         values.  It must examine FEXTRA/XLEN, FNAME, FCOMMENT and FHCRC
         at least so it can skip over the optional fields if they are
         present.  It need not examine any other part of the header or
         trailer; in particular, a decompressor may ignore FTEXT and OS
         and always produce binary output, and still be compliant.  A
         compliant decompressor must give an error indication if any
         reserved bit is non-zero, since such a bit could indicate the
         presence of a new field that would cause subsequent data to be
         interpreted incorrectly.

3. References

   [1] "Information Processing - 8-bit single-byte coded graphic
       character sets - Part 1: Latin alphabet No.1" (ISO 8859-1:1987).
       The ISO 8859-1 (Latin-1) character set is a superset of 7-bit
       ASCII. Files defining this character set are available as
       iso_8859-1.* in ftp://ftp.uu.net/graphics/png/documents/

   [2] ISO 3309

   [3] ITU-T recommendation V.42

   [4] Deutsch, L.P.,"DEFLATE Compressed Data Format Specification",
       available in ftp://ftp.uu.net/pub/archiving/zip/doc/

   [5] Gailly, J.-L., GZIP documentation, available as gzip-*.tar in
       ftp://prep.ai.mit.edu/pub/gnu/

   [6] Sarwate, D.V., "Computation of Cyclic Redundancy Checks via Table
       Look-Up", Communications of the ACM, 31(8), pp.1008-1013.




Deutsch                      Informational                      [Page 9]

RFC 1952             GZIP File Format Specification             May 1996


   [7] Schwaderer, W.D., "CRC Calculation", April 85 PC Tech Journal,
       pp.118-133.

   [8] ftp://ftp.adelaide.edu.au/pub/rocksoft/papers/crc_v3.txt,
       describing the CRC concept.

4. Security Considerations

   Any data compression method involves the reduction of redundancy in
   the data.  Consequently, any corruption of the data is likely to have
   severe effects and be difficult to correct.  Uncompressed text, on
   the other hand, will probably still be readable despite the presence
   of some corrupted bytes.

   It is recommended that systems using this data format provide some
   means of validating the integrity of the compressed data, such as by
   setting and checking the CRC-32 check value.

5. Acknowledgements

   Trademarks cited in this document are the property of their
   respective owners.

   Jean-Loup Gailly designed the gzip format and wrote, with Mark Adler,
   the related software described in this specification.  Glenn
   Randers-Pehrson converted this document to RFC and HTML format.

6. Author's Address

   L. Peter Deutsch
   Aladdin Enterprises
   203 Santa Margarita Ave.
   Menlo Park, CA 94025

   Phone: (415) 322-0103 (AM only)
   FAX:   (415) 322-1734
   EMail: <ghost@aladdin.com>

   Questions about the technical content of this specification can be
   sent by email to:

   Jean-Loup Gailly <gzip@prep.ai.mit.edu> and
   Mark Adler <madler@alumni.caltech.edu>

   Editorial comments on this specification can be sent by email to:

   L. Peter Deutsch <ghost@aladdin.com> and
   Glenn Randers-Pehrson <randeg@alumni.rpi.edu>



Deutsch                      Informational                     [Page 10]

RFC 1952             GZIP File Format Specification             May 1996


7. Appendix: Jean-Loup Gailly's gzip utility

   The most widely used implementation of gzip compression, and the
   original documentation on which this specification is based, were
   created by Jean-Loup Gailly <gzip@prep.ai.mit.edu>.  Since this
   implementation is a de facto standard, we mention some more of its
   features here.  Again, the material in this section is not part of
   the specification per se, and implementations need not follow it to
   be compliant.

   When compressing or decompressing a file, gzip preserves the
   protection, ownership, and modification time attributes on the local
   file system, since there is no provision for representing protection
   attributes in the gzip file format itself.  Since the file format
   includes a modification time, the gzip decompressor provides a
   command line switch that assigns the modification time from the file,
   rather than the local modification time of the compressed input, to
   the decompressed output.

8. Appendix: Sample CRC Code

   The following sample code represents a practical implementation of
   the CRC (Cyclic Redundancy Check). (See also ISO 3309 and ITU-T V.42
   for a formal specification.)

   The sample code is in the ANSI C programming language. Non C users
   may find it easier to read with these hints:

      &      Bitwise AND operator.
      ^      Bitwise exclusive-OR operator.
      >>     Bitwise right shift operator. When applied to an
             unsigned quantity, as here, right shift inserts zero
             bit(s) at the left.
      !      Logical NOT operator.
      ++     "n++" increments the variable n.
      0xNNN  0x introduces a hexadecimal (base 16) constant.
             Suffix L indicates a long value (at least 32 bits).

      /* Table of CRCs of all 8-bit messages. */
      unsigned long crc_table[256];

      /* Flag: has the table been computed? Initially false. */
      int crc_table_computed = 0;

      /* Make the table for a fast CRC. */
      void make_crc_table(void)
      {
        unsigned long c;



Deutsch                      Informational                     [Page 11]

RFC 1952             GZIP File Format Specification             May 1996


        int n, k;
        for (n = 0; n < 256; n++) {
          c = (unsigned long) n;
          for (k = 0; k < 8; k++) {
            if (c & 1) {
              c = 0xedb88320L ^ (c >> 1);
            } else {
              c = c >> 1;
            }
          }
          crc_table[n] = c;
        }
        crc_table_computed = 1;
      }

      /*
         Update a running crc with the bytes buf[0..len-1] and return
       the updated crc. The crc should be initialized to zero. Pre- and
       post-conditioning (one's complement) is performed within this
       function so it shouldn't be done by the caller. Usage example:

         unsigned long crc = 0L;

         while (read_buffer(buffer, length) != EOF) {
           crc = update_crc(crc, buffer, length);
         }
         if (crc != original_crc) error();
      */
      unsigned long update_crc(unsigned long crc,
                      unsigned char *buf, int len)
      {
        unsigned long c = crc ^ 0xffffffffL;
        int n;

        if (!crc_table_computed)
          make_crc_table();
        for (n = 0; n < len; n++) {
          c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
        }
        return c ^ 0xffffffffL;
      }

      /* Return the CRC of the bytes buf[0..len-1]. */
      unsigned long crc(unsigned char *buf, int len)
      {
        return update_crc(0L, buf, len);
      }




Deutsch                      Informational                     [Page 12]


A Fast Method for Identifying Plain Text Files
==============================================


Introduction
------------

Given a file coming from an unknown source, it is sometimes desirable
to find out whether the format of that file is plain text.  Although
this may appear like a simple task, a fully accurate detection of the
file type requires heavy-duty semantic analysis on the file contents.
It is, however, possible to obtain satisfactory results by employing
various heuristics.

Previous versions of PKZip and other zip-compatible compression tools
were using a crude detection scheme: if more than 80% (4/5) of the bytes
found in a certain buffer are within the range [7..127], the file is
labeled as plain text, otherwise it is labeled as binary.  A prominent
limitation of this scheme is the restriction to Latin-based alphabets.
Other alphabets, like Greek, Cyrillic or Asian, make extensive use of
the bytes within the range [128..255], and texts using these alphabets
are most often misidentified by this scheme; in other words, the rate
of false negatives is sometimes too high, which means that the recall
is low.  Another weakness of this scheme is a reduced precision, due to
the false positives that may occur when binary files containing large
amounts of textual characters are misidentified as plain text.

In this article we propose a new, simple detection scheme that features
a much increased precision and a near-100% recall.  This scheme is
designed to work on ASCII, Unicode and other ASCII-derived alphabets,
and it handles single-byte encodings (ISO-8859, MacRoman, KOI8, etc.)
and variable-sized encodings (ISO-2022, UTF-8, etc.).  Wider encodings
(UCS-2/UTF-16 and UCS-4/UTF-32) are not handled, however.


The Algorithm
-------------

The algorithm works by dividing the set of bytecodes [0..255] into three
categories:
- The white list of textual bytecodes:
  9 (TAB), 10 (LF), 13 (CR), 32 (SPACE) to 255.
- The gray list of tolerated bytecodes:
  7 (BEL), 8 (BS), 11 (VT), 12 (FF), 26 (SUB), 27 (ESC).
- The black list of undesired, non-textual bytecodes:
  0 (NUL) to 6, 14 to 31.

If a file contains at least one byte that belongs to the white list and
no byte that belongs to the black list, then the file is categorized as
plain text; otherwise, it is categorized as binary.  (The boundary case,
when the file is empty, automatically falls into the latter category.)


Rationale
---------

The idea behind this algorithm relies on two observations.

The first observation is that, although the full range of 7-bit codes
[0..127] is properly specified by the ASCII standard, most control
characters in the range [0..31] are not used in practice.  The only
widely-used, almost universally-portable control codes are 9 (TAB),
10 (LF) and 13 (CR).  There are a few more control codes that are
recognized on a reduced range of platforms and text viewers/editors:
7 (BEL), 8 (BS), 11 (VT), 12 (FF), 26 (SUB) and 27 (ESC); but these
codes are rarely (if ever) used alone, without being accompanied by
some printable text.  Even the newer, portable text formats such as
XML avoid using control characters outside the list mentioned here.

The second observation is that most of the binary files tend to contain
control characters, especially 0 (NUL).  Even though the older text
detection schemes observe the presence of non-ASCII codes from the range
[128..255], the precision rarely has to suffer if this upper range is
labeled as textual, because the files that are genuinely binary tend to
contain both control characters and codes from the upper range.  On the
other hand, the upper range needs to be labeled as textual, because it
is used by virtually all ASCII extensions.  In particular, this range is
used for encoding non-Latin scripts.

Since there is no counting involved, other than simply observing the
presence or the absence of some byte values, the algorithm produces
consistent results, regardless what alphabet encoding is being used.
(If counting were involved, it could be possible to obtain different
results on a text encoded, say, using ISO-8859-16 versus UTF-8.)

There is an extra category of plain text files that are "polluted" with
one or more black-listed codes, either by mistake or by peculiar design
considerations.  In such cases, a scheme that tolerates a small fraction
of black-listed codes would provide an increased recall (i.e. more true
positives).  This, however, incurs a reduced precision overall, since
false positives are more likely to appear in binary files that contain
large chunks of textual data.  Furthermore, "polluted" plain text should
be regarded as binary by general-purpose text detection schemes, because
general-purpose text processing algorithms might not be applicable.
Under this premise, it is safe to say that our detection method provides
a near-100% recall.

Experiments have been run on many files coming from various platforms
and applications.  We tried plain text files, system logs, source code,
formatted office documents, compiled object code, etc.  The results
confirm the optimistic assumptions about the capabilities of this
algorithm.


--
Cosmin Truta
Last updated: 2006-May-28

\fBTcl_SetVar2Ex\fR).
.PP
A typical usage for \fBTcl_GetReturnOptions\fR is to
retrieve the stack trace when script evaluation returns
\fBTCL_ERROR\fR, like so:
.PP
.CS
int code = Tcl_EvalEx(interp, script, -1, 0);
if (code == TCL_ERROR) {
    Tcl_Obj *options = \fBTcl_GetReturnOptions\fR(interp, code);
    Tcl_Obj *key = Tcl_NewStringObj("-errorinfo", -1);
    Tcl_Obj *stackTrace;
    Tcl_IncrRefCount(key);
    Tcl_DictObjGet(NULL, options, key, &stackTrace);
    Tcl_DecrRefCount(key);

'\"
'\" Copyright (c) 1989-1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_AsyncCreate 3 7.0 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_AsyncCreate, Tcl_AsyncMark, Tcl_AsyncInvoke, Tcl_AsyncDelete, Tcl_AsyncReady \- handle asynchronous events
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_AsyncHandler
\fBTcl_AsyncCreate\fR(\fIproc, clientData\fR)
.sp
\fBTcl_AsyncMark\fR(\fIasync\fR)
.sp



int
\fBTcl_AsyncInvoke\fR(\fIinterp, code\fR)
.sp
\fBTcl_AsyncDelete\fR(\fIasync\fR)
.sp
int
\fBTcl_AsyncReady\fR()
.SH ARGUMENTS
.AS Tcl_AsyncHandler clientData
.AP Tcl_AsyncProc *proc in
Procedure to invoke to handle an asynchronous event.
.AP ClientData clientData in
One-word value to pass to \fIproc\fR.
.AP Tcl_AsyncHandler async in
Token for asynchronous event handler.


.AP Tcl_Interp *interp in
Tcl interpreter in which command was being evaluated when handler was
invoked, or NULL if handler was invoked when there was no interpreter
active.
.AP int code in
Completion code from command that just completed in \fIinterp\fR,
or 0 if \fIinterp\fR is NULL.

allocation could have been in progress when the event occurred.
The only safe approach is to set a flag indicating that the event
occurred, then handle the event later when the world has returned
to a clean state, such as after the current Tcl command completes.
.PP
\fBTcl_AsyncCreate\fR, \fBTcl_AsyncDelete\fR, and \fBTcl_AsyncReady\fR
are thread sensitive.  They access and/or set a thread-specific data
structure in the event of a core built with \fI\-\-enable\-threads\fR.  The token
created by \fBTcl_AsyncCreate\fR contains the needed thread information it
was called from so that calling \fBTcl_AsyncMark\fR(\fItoken\fR) will only yield

the origin thread into the asynchronous handler.
.PP
\fBTcl_AsyncCreate\fR creates an asynchronous handler and returns
a token for it.
The asynchronous handler must be created before
any occurrences of the asynchronous event that it is intended
to handle (it is not safe to create a handler at the time of
an event).
When an asynchronous event occurs the code that detects the event
(such as a signal handler) should call \fBTcl_AsyncMark\fR with the
token for the handler.


\fBTcl_AsyncMark\fR will mark the handler as ready to execute, but it

will not invoke the handler immediately.
Tcl will call the \fIproc\fR associated with the handler later, when
the world is in a safe state, and \fIproc\fR can then carry out
the actions associated with the asynchronous event.
\fIProc\fR should have arguments and result that match the
type \fBTcl_AsyncProc\fR:
.PP
.CS
typedef int \fBTcl_AsyncProc\fR(
        ClientData \fIclientData\fR,
        Tcl_Interp *\fIinterp\fR,

\fBTcl_ExternalToUtf\fR.
.PP
\fBTcl_WinUtfToTChar\fR and \fBTcl_WinTCharToUtf\fR are
Windows-only convenience
functions for converting between UTF-8 and Windows strings
based on the TCHAR type which is by convention
a Unicode character on Windows NT.
These functions are essentially wrappers around
\fBTcl_UtfToExternalDString\fR and
\fBTcl_ExternalToUtfDString\fR that convert to and from the
Unicode encoding.
.PP
\fBTcl_GetEncodingName\fR is roughly the inverse of \fBTcl_GetEncoding\fR.
Given an \fIencoding\fR, the return value is the \fIname\fR argument that
was used to create the encoding.  The string returned by
\fBTcl_GetEncodingName\fR is only guaranteed to persist until the
\fIencoding\fR is deleted.  The caller must not modify this string.
.PP

\fBTCL_EVAL_DIRECT\fR flag is useful in situations where the
contents of a value are going to change immediately, so the
bytecodes will not be reused in a future execution.  In this case,
it is faster to execute the script directly.
.TP 23
\fBTCL_EVAL_GLOBAL\fR
.
If this flag is set, the script is processed at global level.  This
means that it is evaluated in the global namespace and its variable
context consists of global variables only (it ignores any Tcl
procedures that are active).


.SH "MISCELLANEOUS DETAILS"
.PP
During the processing of a Tcl command it is legal to make nested
calls to evaluate other commands (this is how procedures and
some control structures are implemented).
If a code other than \fBTCL_OK\fR is returned

custom set of allocation routines might depend on, in order to avoid any
circular dependency.
.PP
The \fIhashKeyProc\fR member contains the address of a function called to
calculate a hash value for the key.
.PP
.CS
typedef TCL_HASH_TYPE \fBTcl_HashKeyProc\fR(
        Tcl_HashTable *\fItablePtr\fR,
        void *\fIkeyPtr\fR);
.CE
.PP
If this is NULL then \fIkeyPtr\fR is used and
\fBTCL_HASH_KEY_RANDOMIZE_HASH\fR is assumed.
.PP

.AS Tcl_Interp *interp
.AP Tcl_Interp *interp in
Tcl interpreter handle.
.AP "const char" *version in
A version string consisting of one or more decimal numbers
separated by dots.
.AP int exact in
1 means that only the particular version specified by
\fIversion\fR is acceptable.
0 means that versions newer than \fIversion\fR are also
acceptable as long as they have the same major version number
as \fIversion\fR. Other bits have no effect.
.BE
.SH INTRODUCTION
.PP
The Tcl stubs mechanism defines a way to dynamically bind
extensions to a particular Tcl implementation at run time.
This provides two significant benefits to Tcl users:
.IP 1) 5

with which values might be exchanged.  The C integral types for which Tcl
provides value exchange routines are \fBint\fR, \fBlong int\fR,
\fBTcl_WideInt\fR, and \fBmp_int\fR.  The \fBint\fR and \fBlong int\fR types
are provided by the C language standard.  The \fBTcl_WideInt\fR type is a
typedef defined to be whatever signed integral type covers at least the
64-bit integer range (-9223372036854775808 to 9223372036854775807).  Depending
on the platform and the C compiler, the actual type might be
\fBlong int\fR, \fBlong long int\fR, \fBint64\fR, or something else.
The \fBmp_int\fR type is a multiple-precision integer type defined
by the LibTomMath multiple-precision integer library.
.PP
The \fBTcl_NewIntObj\fR, \fBTcl_NewLongObj\fR, \fBTcl_NewWideIntObj\fR,
and \fBTcl_NewBignumObj\fR routines each create and return a new
Tcl value initialized to the integral value of the argument.  The
returned Tcl value is unshared.

.\"
.\" Copyright (c) 2008 by Kevin B. Kenny.

.\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH NRE 3 8.6 Tcl "Tcl Library Procedures"
.so man.macros
.BS

.sp
void
\fBTcl_NRAddCallback\fR(\fIinterp, postProcPtr, data0, data1, data2, data3\fR)
.fi
.SH ARGUMENTS
.AS Tcl_CmdDeleteProc *interp in
.AP Tcl_Interp *interp in
Interpreter in which to create or evaluate a command.
.AP char *cmdName in
Name of a new command to create.
.AP Tcl_ObjCmdProc *proc in
Implementation of a command that will be called whenever \fIcmdName\fR

is invoked as a command in the unoptimized way.

.AP Tcl_ObjCmdProc *nreProc in
Implementation of a command that will be called whenever \fIcmdName\fR
is invoked and requested to conserve the C stack.

.AP ClientData clientData in
Arbitrary one-word value that will be passed to \fIproc\fR, \fInreProc\fR,
\fIdeleteProc\fR and \fIobjProc\fR.
.AP Tcl_CmdDeleteProc *deleteProc in/out
Procedure to call before \fIcmdName\fR is deleted from the interpreter.
This procedure allows for command-specific cleanup. If \fIdeleteProc\fR
is \fBNULL\fR, then no procedure is called before the command is deleted.
.AP int objc in
Count of parameters provided to the implementation of a command.
.AP Tcl_Obj **objv in
Pointer to an array of Tcl values. Each value holds the value of a
single word in the command to execute.
.AP Tcl_Obj *objPtr in
Pointer to a Tcl_Obj whose value is a script or expression to execute.
.AP int flags in

ORed combination of flag bits that specify additional options.
\fBTCL_EVAL_GLOBAL\fR is the only flag that is currently supported.
.\" TODO: This is a lie. But kbk didn't grasp TCL_EVAL_INVOKE and
.\"       TCL_EVAL_NOERR well enough to document them.
.AP Tcl_Command cmd in
Token for a command that is to be used instead of the currently
executing command.
.AP Tcl_Obj *resultPtr out
Pointer to an unshared Tcl_Obj where the result of expression
evaluation is written.
.AP Tcl_NRPostProc *postProcPtr in
Pointer to a function that will be invoked when the command currently
executing in the interpreter designated by \fIinterp\fR completes.
.AP ClientData data0 in
.AP ClientData data1 in
.AP ClientData data2 in
.AP ClientData data3 in
\fIdata0\fR through \fIdata3\fR are four one-word values that will be passed
to the function designated by \fIpostProcPtr\fR when it is invoked.
.BE
.SH DESCRIPTION
.PP
This series of C functions provides an interface whereby commands that

are implemented in C can be evaluated, and invoke Tcl commands scripts



and scripts, without consuming space on the C stack. The non-recursive

evaluation is done by installing a \fItrampoline\fR, a small piece of
code that invokes a command or script, and then executes a series of

callbacks when the command or script returns.
.PP
The \fBTcl_NRCreateCommand\fR function creates a Tcl command in the
interpreter designated by \fIinterp\fR that is prepared to handle
nonrecursive evaluation with a trampoline. The \fIcmdName\fR argument
gives the name of the new command. If \fIcmdName\fR contains any
namespace qualifiers, then the new command is added to the specified
namespace; otherwise, it is added to the global namespace. \fIproc\fR
gives the procedure that will be called when the interpreter wishes to
evaluate the command in an unoptimized manner, and \fInreProc\fR is
the procedure that will be called when the interpreter wishes to
evaluate the command using a trampoline. \fIdeleteProc\fR is a
function that will be called before the command is deleted from the
interpreter. When any of the three functions is invoked, it is passed
the \fIclientData\fR parameter.
.PP
\fBTcl_NRCreateCommand\fR deletes any existing command
\fIname\fR already associated with the interpreter
(however see below for an exception where the existing command
is not deleted).

It returns a token that may be used to refer
to the command in subsequent calls to \fBTcl_GetCommandName\fR.
If \fBTcl_NRCreateCommand\fR is called for an interpreter that is in
the process of being deleted, then it does not create a new command,
does not delete any existing command of the same name, and returns NULL.
.PP
The \fIproc\fR and \fInreProc\fR function are expected to conform to
all the rules set forth for the \fIproc\fR argument to
\fBTcl_CreateObjCommand\fR(3) (\fIq.v.\fR).
.PP
When a command that is written to cope with evaluation via trampoline
is invoked without a trampoline on the stack, it will usually respond
to the invocation by creating a trampoline and calling the
trampoline-enabled implementation of the same command. This call is done by
means of \fBTcl_NRCallObjProc\fR. In the call to
\fBTcl_NRCallObjProc\fR, the \fIinterp\fR, \fIclientData\fR,
\fIobjc\fR and \fIobjv\fR parameters should be the same ones that were
passed to \fIproc\fR. The \fInreProc\fR parameter should designate the
trampoline-enabled implementation of the command.
.PP
\fBTcl_NREvalObj\fR arranges for the script contained in \fIobjPtr\fR
to be evaluated in the interpreter designated by \fIinterp\fR after
the current command (which must be trampoline-enabled) returns. It is
the method by which a command may invoke a script without consuming


space on the C stack. Similarly, \fBTcl_NREvalObjv\fR arranges to
invoke a single Tcl command whose words have already been separated
and substituted. The \fIobjc\fR and \fIobjv\fR parameters give the
words of the command to be evaluated when execution reaches the
trampoline.
.PP
\fBTcl_NRCmdSwap\fR allows for trampoline evaluation of a command whose
resolution is already known.  The \fIcmd\fR parameter gives a
\fBTcl_Command\fR token (returned from \fBTcl_CreateObjCommand\fR or
\fBTcl_GetCommandFromObj\fR) identifying the command to be invoked in
the trampoline; this command must match the word in \fIobjv[0]\fR.
The remaining arguments are as for \fBTcl_NREvalObjv\fR.

.PP
\fBTcl_NREvalObj\fR, \fBTcl_NREvalObjv\fR and \fBTcl_NRCmdSwap\fR
all accept a \fIflags\fR parameter, which is an OR-ed-together set of
bits to control evaluation. At the present time, the only supported flag
available to callers is \fBTCL_EVAL_GLOBAL\fR.
.\" TODO: Again, this is a lie. Do we want to explain TCL_EVAL_INVOKE
.\"       and TCL_EVAL_NOERR?

If the \fBTCL_EVAL_GLOBAL\fR flag is set, the script or command is
evaluated in the global namespace. If it is not set, it is evaluated
in the current namespace.
.PP
\fBTcl_NRExprObj\fR arranges for the expression contained in \fIobjPtr\fR
to be evaluated in the interpreter designated by \fIinterp\fR after
the current command (which must be trampoline-enabled) returns. It is
the method by which a command may evaluate a Tcl expression without consuming
space on the C stack.  The argument \fIresultPtr\fR is a pointer to an
unshared Tcl_Obj where the result of expression evaluation is to be written.
If expression evaluation returns any code other than TCL_OK, the
\fIresultPtr\fR value is left untouched.
.PP
All of the routines return \fBTCL_OK\fR if command or expression invocation
has been scheduled successfully. If for any reason the scheduling cannot
be completed (for example, if the interpreter is unable to find
the requested command), they return \fBTCL_ERROR\fR with an
appropriate message left in the interpreter's result.
.PP
\fBTcl_NRAddCallback\fR arranges to have a C function called when the
current trampoline-enabled command in the Tcl interpreter designated
by \fIinterp\fR returns.  The \fIpostProcPtr\fR argument is a pointer
to the callback function, which must have arguments and return value
consistent with the \fBTcl_NRPostProc\fR data type:
.PP
.CS
typedef int
\fBTcl_NRPostProc\fR(
        \fBClientData\fR \fIdata\fR[],
        \fBTcl_Interp\fR *\fIinterp\fR,
        int \fIresult\fR);
.CE
.PP
When the trampoline invokes the callback function, the \fIdata\fR
parameter will point to an array containing the four one-word
quantities that were passed to \fBTcl_NRAddCallback\fR in the
\fIdata0\fR through \fIdata3\fR parameters. The Tcl interpreter will
be designated by the \fIinterp\fR parameter, and the \fIresult\fR
parameter will contain the result (\fBTCL_OK\fR, \fBTCL_ERROR\fR,
\fBTCL_RETURN\fR, \fBTCL_BREAK\fR or \fBTCL_CONTINUE\fR) that was
returned by the command evaluation. The callback function is expected,
in turn, either to return a \fIresult\fR to control further evaluation.
.PP
Multiple \fBTcl_NRAddCallback\fR invocations may request multiple
callbacks, which may be to the same or different callback
functions. If multiple callbacks are requested, they are executed in
last-in, first-out order, that is, the most recently requested
callback is executed first.
.SH EXAMPLE
.PP
The usual pattern for Tcl commands that invoke other Tcl commands
is something like:

.PP
.CS
int
\fITheCmdOldObjProc\fR(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,

    return result;
}
\fBTcl_CreateObjCommand\fR(interp, "theCommand",
        \fITheCmdOldObjProc\fR, clientData, TheCmdDeleteProc);
.CE
.PP
To enable a command like this one for trampoline-based evaluation,
it must be split into three pieces:
.IP \(bu
A non-trampoline implementation, \fITheCmdNewObjProc\fR,
which will simply create a trampoline
and invoke the trampoline-based implementation.
.IP \(bu

A trampoline-enabled implementation, \fITheCmdNRObjProc\fR.  This
function will perform the initialization, request that the trampoline
call the postprocessing routine after command evaluation, and finally,
request that the trampoline call the inner command.
.IP \(bu
A postprocessing routine, \fITheCmdPostProc\fR. This function will
perform the postprocessing formerly done after the return from the
inner command in \fITheCmdObjProc\fR.
.PP
The non-trampoline implementation is simple and stylized, containing
a single statement:
.PP
.CS
int
\fITheCmdNewObjProc\fR(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    return \fBTcl_NRCallObjProc\fR(interp, \fITheCmdNRObjProc\fR,
            clientData, objc, objv);
}
.CE
.PP
The trampoline-enabled implementation requests postprocessing,
and returns to the trampoline requesting command evaluation.
.PP
.CS
int
\fITheCmdNRObjProc\fR
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const objv[])
{
    Tcl_Obj *objPtr;

    \fI... preparation ...\fR

    \fBTcl_NRAddCallback\fR(interp, \fITheCmdPostProc\fR,
            data0, data1, data2, data3);
    /* \fIdata0 .. data3\fR are up to four one-word items to
     * pass to the postprocessing procedure */

    return \fBTcl_NREvalObj\fR(interp, objPtr, 0);
}
.CE
.PP
The postprocessing procedure does whatever the original command did
upon return from the inner evaluation.
.PP
.CS
int
\fITheCmdNRPostProc\fR(
    ClientData data[],
    Tcl_Interp *interp,
    int result)
{
    /* \fIdata[0] .. data[3]\fR are the four words of data
     * passed to \fBTcl_NRAddCallback\fR */

    \fI... postprocessing ...\fR

    return result;
}
.CE
.PP
If \fItheCommand\fR is a command that results in multiple commands or
scripts being evaluated, its postprocessing routine may schedule
additional postprocessing and then request another command evaluation
by means of \fBTcl_NREvalObj\fR or one of the other evaluation
routines. Looping and sequencing constructs may be implemented in this way.
.PP
Finally, to install a trampoline-enabled command in the interpreter,
\fBTcl_NRCreateCommand\fR is used in place of
\fBTcl_CreateObjCommand\fR.  It accepts two command procedures instead
of one. The first is for use when no trampoline is yet on the stack,
and the second is for use when there is already a trampoline in place.
.PP
.CS
\fBTcl_NRCreateCommand\fR(interp, "theCommand",
        \fITheCmdNewObjProc\fR, \fITheCmdNRObjProc\fR, clientData,
        TheCmdDeleteProc);
.CE
.SH "SEE ALSO"
Tcl_CreateCommand(3), Tcl_CreateObjCommand(3), Tcl_EvalObjEx(3), Tcl_GetCommandFromObj(3), Tcl_ExprObj(3)
.SH KEYWORDS
stackless, nonrecursive, execute, command, global, value, result, script
.SH COPYRIGHT
Copyright (c) 2008 by Kevin B. Kenny

\fBincr x\fR
.CE
.PP
The \fBincr\fR command first gets an integer from \fIx\fR's value
by calling \fBTcl_GetIntFromObj\fR.
This procedure checks whether the value is already an integer value.
Since it is not, it converts the value
by setting the value's \fIinternalRep.longValue\fR member
to the integer \fB123\fR
and setting the value's \fItypePtr\fR
to point to the integer Tcl_ObjType structure.
Both representations are now valid.
\fBincr\fR increments the value's integer internal representation
then invalidates its string representation
(by calling \fBTcl_InvalidateStringRep\fR)

'\"
'\" Copyright (c) 1996-7 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_OpenTcpClient 3 8.7 Tcl "Tcl Library Procedures"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
Tcl_OpenTcpClient, Tcl_MakeTcpClientChannel, Tcl_OpenTcpServer, Tcl_OpenTcpServerEx \- procedures to open channels using TCP sockets
.SH SYNOPSIS
.nf
\fB#include <tcl.h> \fR
.sp
Tcl_Channel
\fBTcl_OpenTcpClient\fR(\fIinterp, port, host, myaddr, myport, async\fR)
.sp
Tcl_Channel
\fBTcl_MakeTcpClientChannel\fR(\fIsock\fR)
.sp
Tcl_Channel
\fBTcl_OpenTcpServer\fR(\fIinterp, port, myaddr, proc, clientData\fR)
.sp
Tcl_Channel
\fBTcl_OpenTcpServerEx\fR(\fIinterp, service, myaddr, flags, proc, clientData\fR)
.sp
.SH ARGUMENTS
.AS Tcl_TcpAcceptProc clientData
.AP Tcl_Interp *interp in
Tcl interpreter to use for error reporting.  If non-NULL and an
error occurs, an error message is left in the interpreter's result.
.AP int port in
A port number to connect to as a client or to listen on as a server.
.AP "const char" *service in
A string specifying the port number to connect to as a client or to listen on as
 a server.
.AP "const char" *host in
A string specifying a host name or address for the remote end of the connection.
.AP int myport in
A port number for the client's end of the socket.  If 0, a port number
is allocated at random.
.AP "const char" *myaddr in
A string specifying the host name or address for network interface to use
for the local end of the connection.  If NULL, a default interface is
chosen.
.AP int async in
If nonzero, the client socket is connected asynchronously to the server.
.AP "unsigned int" flags in
ORed combination of \fBTCL_TCPSERVER\fR flags that specify additional
informations about the socket being created.
.AP ClientData sock in
Platform-specific handle for client TCP socket.
.AP Tcl_TcpAcceptProc *proc in
Pointer to a procedure to invoke each time a new connection is
accepted via the socket.
.AP ClientData clientData in
Arbitrary one-word value to pass to \fIproc\fR.

a remote client is pending.
.PP
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR.
If one of the standard channels, \fBstdin\fR, \fBstdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.
.SS TCL_OPENTCPSERVEREX
.PP
\fBTcl_OpenTcpServerEx\fR behaviour is identical to \fBTcl_OpenTcpServer\fR but
gives more flexibility to the user by providing a mean to further customize some
aspects of the socket via the \fIflags\fR parameter.
.SH "PLATFORM ISSUES"
.PP
On Unix platforms, the socket handle is a Unix file descriptor as
returned by the \fBsocket\fR system call.  On the Windows platform, the
socket handle is a \fBSOCKET\fR as defined in the WinSock API.
.SH "SEE ALSO"
Tcl_OpenFileChannel(3), Tcl_RegisterChannel(3), vwait(n)
.SH KEYWORDS
channel, client, server, socket, TCP

As noted above, the \fItype\fR field is used to describe the interpretation of
the argument's value. The following values are acceptable values for
\fItype\fR:
.TP
\fBTCL_ARGV_CONSTANT\fR
.
The argument does not take any following value argument. If this argument is
present, the int pointed to by the \fIsrcPtr\fR field is copied to the
\fIdstPtr\fR field. The \fIclientData\fR field is ignored.
.TP
\fBTCL_ARGV_END\fR
.
This value marks the end of all option descriptors in the table. All other
fields are ignored.
.TP
\fBTCL_ARGV_FLOAT\fR

value may then be passed back to one of \fBTcl_RestoreInterpState\fR
or \fBTcl_DiscardInterpState\fR, depending on whether the interp
state is to be restored.  So long as one of the latter two routines
is called, Tcl will take care of memory management.
.PP
The second triplet stores the snapshot of only the interpreter
result (not its complete state) in memory allocated by the caller.
These routines are passed a pointer to a \fBTcl_SavedResult\fR structure
that is used to store enough information to restore the interpreter result.
This structure can be allocated on the stack of the calling
procedure.  These routines do not save the state of any error
information in the interpreter (e.g. the \fB\-errorcode\fR or
\fB\-errorinfo\fR return options, when an error is in progress).
.PP
Because the routines \fBTcl_SaveInterpState\fR,
\fBTcl_RestoreInterpState\fR, and \fBTcl_DiscardInterpState\fR perform
a superset of the functions provided by the other routines,

\fBTcl_UtfToLower\fR(\fIstr\fR)
.sp
int
\fBTcl_UtfToTitle\fR(\fIstr\fR)
.SH ARGUMENTS
.AS char *str in/out
.AP int ch in
The Tcl_UniChar to be converted.
.AP char *str in/out
Pointer to UTF-8 string to be converted in place.
.BE

.SH DESCRIPTION
.PP
The first three routines convert the case of individual Unicode characters:

.PP
\fBTcl_UtfToTitle\fR is the same as \fBTcl_UtfToUpper\fR except it
turns the first character in the string into its title-case equivalent
and all following characters into their lower-case equivalents.

.SH BUGS
.PP
At this time, the case conversions are only defined for the ISO8859-1
characters.  Unicode characters above 0x00ff are not modified by these
routines.


.SH KEYWORDS
utf, unicode, toupper, tolower, totitle, case

.AS int ch
.AP int ch in
The Tcl_UniChar to be examined.
.BE

.SH DESCRIPTION
.PP
All of the routines described examine Tcl_UniChars and return a
boolean value. A non-zero return value means that the character does
belong to the character class associated with the called routine. The
rest of this document just describes the character classes associated
with the various routines.
.PP
Note: A Tcl_UniChar is a Unicode character represented as an unsigned,
fixed-size quantity.

.SH "CHARACTER CLASSES"
.PP
\fBTcl_UniCharIsAlnum\fR tests if the character is an alphanumeric Unicode character.
.PP
\fBTcl_UniCharIsAlpha\fR tests if the character is an alphabetic Unicode character.
.PP

\fBTcl_UtfBackslash\fR(\fIsrc, readPtr, dst\fR)
.SH ARGUMENTS
.AS "const Tcl_UniChar" *uniPattern in/out
.AP char *buf out
Buffer in which the UTF-8 representation of the Tcl_UniChar is stored.  At most
\fBTCL_UTF_MAX\fR bytes are stored in the buffer.
.AP int ch in
The Tcl_UniChar to be converted or examined.
.AP Tcl_UniChar *chPtr out
Filled with the Tcl_UniChar represented by the head of the UTF-8 string.
.AP "const char" *src in
Pointer to a UTF-8 string.
.AP "const char" *cs in
Pointer to a UTF-8 string.
.AP "const char" *ct in

.SH NAME
after \- Execute a command after a time delay
.SH SYNOPSIS
\fBafter \fIms\fR
.sp
\fBafter \fIms \fR?\fIscript script script ...\fR?
.sp


\fBafter cancel \fIid\fR
.sp
\fBafter cancel \fIscript script script ...\fR
.sp
\fBafter idle \fR?\fIscript script script ...\fR?
.sp
\fBafter info \fR?\fIid\fR?

The command will be executed at global level (outside the context
of any Tcl procedure).
If an error occurs while executing the delayed command then
the background error will be reported by the command
registered with \fBinterp bgerror\fR.
The \fBafter\fR command returns an identifier that can be used
to cancel the delayed command using \fBafter cancel\fR.















.TP
\fBafter cancel \fIid\fR
.
Cancels the execution of a delayed command that
was previously scheduled.
\fIId\fR indicates which command should be canceled;  it must have
been the return value from a previous \fBafter\fR command.

exactly 86400 seconds.  Tcl responds to leap seconds by speeding or
slowing its clock by a tiny fraction for some minutes until it is
back in sync with UTC; its data model does not represent minutes that
have 59 or 61 seconds.
.TP
\fIunit\fR
One of the words, \fBseconds\fR, \fBminutes\fR, \fBhours\fR,
\fBdays\fR, \fBweekdays\fR, \fBweeks\fR, \fBmonths\fR, or \fByears\fR.
Used in conjunction with \fIcount\fR to identify an interval of time,
for example, \fI3 seconds\fR or \fI1 year\fR.

.SS "OPTIONS"
.TP
\fB\-base\fR time
Specifies that any relative times present in a \fBclock scan\fR command
are to be given relative to \fItime\fR.  \fItime\fR must be expressed as
a count of nominal seconds from the epoch time of 1 January 1970, 00:00 UTC.
.TP

.PP
The \fBclock add\fR command performs clock arithmetic on a value
(expressed as nominal seconds from the epoch time of 1 January 1970, 00:00 UTC)
given as its first argument.  The remaining arguments (other than the
possible \fB\-timezone\fR, \fB\-locale\fR and \fB\-gmt\fR options)
are integers and keywords in alternation, where the keywords are chosen
from \fBseconds\fR, \fBminutes\fR, \fBhours\fR,
\fBdays\fR, \fBweekdays\fR, \fBweeks\fR, \fBmonths\fR, or \fByears\fR.

.PP
Addition of seconds, minutes and hours is fairly straightforward;
the given time increment (times sixty for minutes, or 3600 for hours)
is simply added to the \fItimeVal\fR given
to the \fBclock add\fR command.  The result is interpreted as
a nominal number of seconds from the Epoch.
.PP

.CE
.PP
Adding and subtracting days and weeks is accomplished by converting
the given time to a calendar day and time of day in the appropriate
time zone and locale.  The requisite number of days (weeks are converted
to days by multiplying by seven) is added to the calendar day, and
the date and time are then converted back to a count of seconds from
the epoch time.  The \fBweekdays\fR keyword is similar to \fBdays\fR,
with the only difference that weekends - Saturdays and Sundays - are skipped.
.PP
Adding and subtracting a given number of days across the point that
the time changes at the start or end of summer time (Daylight Saving Time)
results in the \fIsame local time\fR on the day in question.  For
instance, the following code sets the value of \fBx\fR to \fB05:00:00\fR.
.PP
.CS

If a format string lacks a \fB%z\fR or \fB%Z\fR format group,
it is possible for the time to be ambiguous because it appears twice
in the same day, once without and once with Daylight Saving Time.
If this situation occurs, the first occurrence of the time is chosen.
(For this reason, it is wise to have the input string contain the
time zone when converting local times.  This caveat does not apply to
UTC times.)













.SH "FORMAT GROUPS"
.PP
The following format groups are recognized by the \fBclock scan\fR and
\fBclock format\fR commands.
.TP
\fB%a\fR
On output, receives an abbreviation (\fIe.g.,\fR \fBMon\fR) for the day

'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
oo::copy \- create copies of objects and classes
.SH SYNOPSIS
.nf
package require TclOO

\fBoo::copy\fI sourceObject \fR?\fItargetObject\fR?
.fi
.BE
.SH DESCRIPTION
.PP
The \fBoo::copy\fR command creates a copy of an object or class. It takes the
name of the object or class to be copied, \fIsourceObject\fR, and optionally
the name of the object or class to create, \fItargetObject\fR, which will be
resolved relative to the current namespace if not an absolute qualified name.






If \fItargetObject\fR is omitted, a new name is chosen. The copied object will



be of the same class as the source object, and will have all its per-object
methods copied. If it is a class, it will also have all the class methods in
the class copied, but it will not have any of its instances copied.

.PP
.VS
After the \fItargetObject\fR has been created and all definitions of its
configuration (e.g., methods, filters, mixins) copied, the \fB<cloned>\fR
method of \fItargetObject\fR will be invoked, to allow for customization of
the created object such as installing related variable traces. The only
argument given will be \fIsourceObject\fR. The default implementation of this

command) will be \fIargList\fR, and the body of the constructor will be
\fIbodyScript\fR. When the body of the constructor is evaluated, the current
namespace of the constructor will be a namespace that is unique to the object
being constructed. Within the constructor, the \fBnext\fR command should be
used to call the superclasses' constructors. If \fIbodyScript\fR is the empty
string, the constructor will be deleted.
.TP
\fBdeletemethod\fI name\fR ?\fIname ...\fR
.
This deletes each of the methods called \fIname\fR from a class. The methods
must have previously existed in that class. Does not affect the superclasses
of the class, nor does it affect the subclasses or instances of the class
(except when they have a call chain through the class being modified).
.TP
\fBdestructor\fI bodyScript\fR

.CS
set foo {foo {a b} bar 2 baz 3}
\fBdict with\fR foo {}
puts $foo
#    prints: \fIa b foo {a b} bar 2 baz 3\fR
.CE
.SH "SEE ALSO"
append(n), array(n), foreach(n), mapeach(n), incr(n), list(n), lappend(n), set(n)
.SH KEYWORDS
dictionary, create, update, lookup, iterate, filter, map
'\" Local Variables:
'\" mode: nroff
'\" End:

.QW \fB@\0\fIfileId\fR
notation, does not work.  When reading from a socket, a 16-bit DOS
application will hang and a 32-bit application will return immediately with
end-of-file.  When either type of application writes to a socket, the
information is instead sent to the console, if one is present, or is
discarded.
.RS













.PP
The Tk console text widget does not provide real standard IO capabilities.
Under Tk, when redirecting from standard input, all applications will see an
immediate end-of-file; information redirected to standard output or standard
error will be discarded.
.PP
Either forward or backward slashes are accepted as path separators for

.CS
\fBexec\fR cmp.bat somefile.c -o somefile
.CE
.PP
With the file \fIcmp.bat\fR looking something like:
.PP
.CS




@gcc %1 %2 %3 %4 %5 %6 %7 %8 %9
.CE
.SS "WORKING WITH COMMAND BUILT-INS"
.PP
Sometimes you need to be careful, as different programs may have the
same name and be in the path. It can then happen that typing a command
at the DOS prompt finds \fIa different program\fR than the same

.SH NAME
expr \- Evaluate an expression
.SH SYNOPSIS
\fBexpr \fIarg \fR?\fIarg arg ...\fR?
.BE
.SH DESCRIPTION
.PP
Concatenates \fIarg\fRs, separated by a space, into an expression, and evaluates
that expression, returning its value.
The operators permitted in an expression include a subset of
the operators permitted in C expressions.  For those operators
common to both Tcl and C, Tcl applies the same meaning and precedence
as the corresponding C operators.
The value of an expression is often a numeric result, either an integer or a
floating-point value, but may also be a non-numeric value.
For example, the expression
.PP
.CS
\fBexpr\fR 8.2 + 6
.CE
.PP
evaluates to 14.2.
Expressions differ from C expressions in the way that
operands are specified.  Expressions also support
non-numeric operands, string comparisons, and some
additional operators not found in C.
.PP
When an expression evaluates to an integer, the value is the decimal form of
the integer, and when an expression evaluates to a floating-point number, the
value is the form produced by the \fB%g\fR format specifier of Tcl's
\fBformat\fR command.
.SS OPERANDS
.PP
An expression consists of a combination of operands, operators, parentheses and
commas, possibly with whitespace between any of these elements, which is

ignored.

An integer operand may be specified in decimal, binary
(the first two characters are \fB0b\fR), octal
(the first two characters are \fB0o\fR), or hexadecimal
(the first two characters are \fB0x\fR) form.  For
compatibility with older Tcl releases, an operand that begins with \fB0\fR is

interpreted as an octal integer even if the second character is not \fBo\fR.


A floating-point number may be specified in any of several
common decimal formats, and may use the decimal point \fB.\fR,
\fBe\fR or \fBE\fR for scientific notation, and
the sign characters \fB+\fR and \fB\-\fR.  The
following are all valid floating-point numbers:  2.1, 3., 6e4, 7.91e+16.
The strings \fBInf\fR
and \fBNaN\fR, in any combination of case, are also recognized as floating point
values.  An operand that doesn't have a numeric interpretation must be quoted

with either braces or with double quotes.

.PP
An operand may be specified in any of the following ways:
.IP [1]
As a numeric value, either integer or floating-point.
.IP [2]
As a boolean value, using any form understood by \fBstring is\fR
\fBboolean\fR.
.IP [3]
As a variable, using standard \fB$\fR notation.
The value of the variable is then the value of the operand.
.IP [4]
As a string enclosed in double-quotes.
Backslash, variable, and command substitution are performed as described in
\fBTcl\fR.

.IP [5]
As a string enclosed in braces.

The operand is treated as a braced value as described in \fBTcl\fR.
.IP [6]
As a Tcl command enclosed in brackets.
Command substitution is performed as described in \fBTcl\fR.

.IP [7]
As a mathematical function such as \fBsin($x)\fR, whose arguments have any of the above
forms for operands.  See \fBMATH FUNCTIONS\fR below for
a discussion of how mathematical functions are handled.
.PP
Because \fBexpr\fR parses and performs substitutions on values that have



already been parsed and substituted by \fBTcl\fR, it is usually best to enclose
expressions in braces to avoid the first round of substitutions by
\fBTcl\fR.

.PP
Below are some examples of simple expressions where the value of \fBa\fR is 3


and the value of \fBb\fR is 6.  The command on the left side of each line
produces the value on the right side.
.PP
.CS
.ta 6c
\fBexpr\fR 3.1 + $a	\fI6.1\fR
\fBexpr\fR 2 + "$a.$b"	\fI5.6\fR
\fBexpr\fR 4*[llength "6 2"]	\fI8\fR
\fBexpr\fR {{word one} < "word $a"}	\fI0\fR
.CE
.SS OPERATORS
.PP
For operators having both a numeric mode and a string mode, the numeric mode is
chosen when all operands have a numeric interpretation.  The integer
interpretation of an operand is preferred over the floating-point
interpretation.  To ensure string operations on arbitrary values it is generally a
good idea to use \fBeq\fR, \fBne\fR, or the \fBstring\fR command instead of
more versatile operators such as \fB==\fR.
.PP
Unless otherwise specified, operators accept non-numeric operands.  The value
of a boolean operation is 1 if true, 0 otherwise.  See also \fBstring is\fR
\fBboolean\fR.  The valid operators, most of which are also available as
commands in the \fBtcl::mathop\fR namespace (see \fBmathop\fR(n)), are listed
below, grouped in decreasing order of precedence:
.TP 20
\fB\-\0\0+\0\0~\0\0!\fR
.
Unary minus, unary plus, bit-wise NOT, logical NOT.  These operators
may only be applied to numeric operands, and bit-wise NOT may only be
applied to integers.
.TP 20
\fB**\fR
.
Exponentiation.  Valid for numeric operands.

.TP 20
\fB*\0\0/\0\0%\fR
.

Multiply and divide, which are valid for numeric operands, and remainder, which
is valid for integers.  The remainder, an absolute value smaller than the
absolute value of the divisor, has the same sign as the divisor.

.RS
.PP
When applied to integers, division and remainder can be
considered to partition the number line into a sequence of
adjacent non-overlapping pieces, where each piece is the size of the divisor;
the quotient identifies which piece the dividend lies within, and the
remainder identifies where within that piece the dividend lies. A
consequence of this is that the result of
.QW "-57 \fB/\fR 10"
is always -6, and the result of
.QW "-57 \fB%\fR 10"
is always 3.
.RE
.TP 20
\fB+\0\0\-\fR
.
Add and subtract.  Valid for numeric operands.
.TP 20
\fB<<\0\0>>\fR
.
Left and right shift.  Valid for integers.
A right shift always propagates the sign bit.
.TP 20
\fB<\0\0>\0\0<=\0\0>=\fR
.
Boolean less than, greater than, less than or equal, and greater than or equal.



.TP 20
\fB==\0\0!=\fR
.
Boolean equal and not equal.

.TP 20
\fBeq\0\0ne\fR
.
Boolean string equal and string not equal.

.TP 20
\fBin\0\0ni\fR
.
List containment and negated list containment.  The first argument is

interpreted as a string, the second as a list.  \fBin\fR tests for membership

in the list, and \fBni\fR is the inverse.
.TP 20
\fB&\fR
.
Bit-wise AND.  Valid for integer operands.
.TP 20
\fB^\fR
.
Bit-wise exclusive OR.  Valid for integer operands.
.TP 20
\fB|\fR
.
Bit-wise OR.  Valid for integer operands.
.TP 20
\fB&&\fR
.
Logical AND.  If both operands are true, the result is 1, or 0 otherwise.


.TP 20
\fB||\fR
.
Logical OR.  If both operands are false, the result is 0, or 1 otherwise.

.TP 20
\fIx\fB?\fIy\fB:\fIz\fR
.
If-then-else, as in C.  If \fIx\fR is false , the result is the value of

\fIy\fR.  Otherwise the result is the value of \fIz\fR.

.PP


The exponentiation operator promotes types in the same way that the multiply
and divide operators do, and the result is is the same as the result of
\fBpow\fR.
Exponentiation groups right-to-left within a precedence level. Other binary
operators group left-to-right.  For example, the value of
.PP
.CS
\fBexpr\fR {4*2 < 7}
.CE
.PP
is 0, while the value of
.PP
.CS
\fBexpr\fR {2**3**2}
.CE
.PP
is 512.
.PP
As in C, \fB&&\fR, \fB||\fR, and \fB?:\fR feature
.QW "lazy evaluation" ,
which means that operands are not evaluated if they are
not needed to determine the outcome.  For example, in
.PP
.CS
\fBexpr\fR {$v ? [a] : [b]}
.CE
.PP
only one of \fB[a]\fR or \fB[b]\fR is evaluated,




depending on the value of \fB$v\fR.  This is not true of the normal Tcl parser,
so it is normally recommended to enclose the arguments to \fBexpr\fR in braces.
Without braces, as in

\fBexpr\fR $v ? [a] : [b]

both \fB[a]\fR and \fB[b]\fR are evaluated before \fBexpr\fR is even called.
.PP
For more details on the results
produced by each operator, see the documentation for C.
.SS "MATH FUNCTIONS"
.PP

A mathematical function such as \fBsin($x)\fR is replaced with a call to an ordinary
Tcl command in the \fBtcl::mathfunc\fR namespace.  The evaluation
of an expression such as
.PP
.CS
\fBexpr\fR {sin($x+$y)}
.CE
.PP
is the same in every way as the evaluation of
.PP
.CS
\fBexpr\fR {[tcl::mathfunc::sin [\fBexpr\fR {$x+$y}]]}
.CE
.PP
which in turn is the same as the evaluation of
.PP
.CS
tcl::mathfunc::sin [\fBexpr\fR {$x+$y}]
.CE
.PP
\fBtcl::mathfunc::sin\fR is resolved as described in
\fBNAMESPACE RESOLUTION\fR in the \fBnamespace\fR(n) documentation.   Given the
default value of \fBnamespace path\fR, \fB[namespace
current]::tcl::mathfunc::sin\fR or \fB::tcl::mathfunc::sin\fR are the typical
resolutions.
.PP
As in C, a mathematical function may accept multiple arguments separated by commas. Thus,
.PP
.CS
\fBexpr\fR {hypot($x,$y)}
.CE
.PP
becomes
.PP
.CS
tcl::mathfunc::hypot $x $y
.CE
.PP
See the \fBmathfunc\fR(n) documentation for the math functions that are
available by default.
.SS "TYPES, OVERFLOW, AND PRECISION"
.PP
When needed to guarantee exact performance, internal computations involving
integers use the LibTomMath multiple precision integer library.  In Tcl releases

prior to 8.5, integer calculations were performed using one of the C types
\fIlong int\fR or \fITcl_WideInt\fR, causing implicit range truncation
in those calculations where values overflowed the range of those types.
Any code that relied on these implicit truncations should instead call
\fBint()\fR or \fBwide()\fR, which do truncate.

.PP
Internal floating-point computations are
performed using the \fIdouble\fR C type.
When converting a string to floating-point value, exponent overflow is
detected and results in the \fIdouble\fR value of \fBInf\fR or
\fB\-Inf\fR as appropriate.  Floating-point overflow and underflow
are detected to the degree supported by the hardware, which is generally
fairly reliable.
.PP
Conversion among internal representations for integer, floating-point, and
string operands is done automatically as needed.  For arithmetic computations,

integers are used until some floating-point number is introduced, after which
floating-point values are used.  For example,
.PP
.CS
\fBexpr\fR {5 / 4}
.CE
.PP
returns 1, while
.PP
.CS
\fBexpr\fR {5 / 4.0}
\fBexpr\fR {5 / ( [string length "abcd"] + 0.0 )}
.CE
.PP
both return 1.25.
A floating-point result can be distinguished from an integer result by the
presence of either
.QW \fB.\fR
or
.QW \fBe\fR
.PP
. For example,
.PP
.CS
\fBexpr\fR {20.0/5.0}
.CE
.PP
returns \fB4.0\fR, not \fB4\fR.



























.SH "PERFORMANCE CONSIDERATIONS"
.PP
Where an expression contains syntax that Tcl would otherwise perform
substitutions on, enclosing an expression in braces or otherwise quoting it
so that it's a static value allows the Tcl compiler to generate bytecode for
the expression, resulting in better speed and smaller storage requirements.
This also avoids issues that can arise if Tcl is allowed to perform
substitution on the value before \fBexpr\fR is called.
.PP
In the following example, the value of the expression is 11 because the Tcl parser first
substitutes \fB$b\fR and \fBexpr\fR then substitutes \fB$a\fR.  Enclosing the
expression in braces would result in a syntax error.


.CS
set a 3
set b {$a + 2}
\fBexpr\fR $b*4
.CE
.PP

When an expression is generated at runtime, like the one above is, the bytcode
compiler must ensure that new code is generated each time the expression
is evaluated.  This is the most costly kind of expression from a performance
perspective.  In such cases, consider directly using the commands described in
the \fBmathfunc\fR(n) or \fBmathop\fR(n) documentation instead of \fBexpr\fR.

Most expressions are not formed at runtime, but are literal strings or contain


substitutions that don't introduce other substitutions.  To allow the bytecode
compiler to work with an expression as a string literal at compilation time,
ensure that it contains no substitutions or that it is enclosed in braces or
otherwise quoted to prevent Tcl from performing substitutions, allowing
\fBexpr\fR to perform them instead.







.SH EXAMPLES
.PP
A numeric comparison whose result is 1:
.CS
\fBexpr\fR {"0x03" > "2"}
.CE
.PP
A string comparison whose result is 1:
.CS
\fBexpr\fR {"0y" > "0x12"}
.CE
.PP
Define a procedure that computes an
.QW interesting
mathematical function:
.PP
.CS
proc tcl::mathfunc::calc {x y} {

Print a message describing the relationship of two string values to
each other:
.PP
.CS
puts "a and b are [\fBexpr\fR {$a eq $b ? {equal} : {different}}]"
.CE
.PP
Set a variable indicating whether an environment variable is defined and has
value of true:
.PP
.CS
set isTrue [\fBexpr\fR {
    [info exists ::env(SOME_ENV_VAR)] &&
    [string is true -strict $::env(SOME_ENV_VAR)]
}]
.CE

returns
.QW \fB/\0\0foo\0\0./~bar\0\0baz\fR
to ensure that later commands
that use the third component do not attempt to perform tilde
substitution.
.RE
.TP
\fBfile stat \fIname varName\fR
.
Invokes the \fBstat\fR kernel call on \fIname\fR, and uses the variable
given by \fIvarName\fR to hold information returned from the kernel call.
\fIVarName\fR is treated as an array variable, and the following elements
of that variable are set: \fBatime\fR, \fBctime\fR, \fBdev\fR, \fBgid\fR,
\fBino\fR, \fBmode\fR, \fBmtime\fR, \fBnlink\fR, \fBsize\fR, \fBtype\fR,
\fBuid\fR.  Each element except \fBtype\fR is a decimal string with the

number if the first character is not a sign.
.TP 10
\fB0\fR
Specifies that the number should be padded on the left with
zeroes instead of spaces.
.TP 10
\fB#\fR
Requests an alternate output form. For \fBo\fR and \fBO\fR
conversions it guarantees that the first digit is always \fB0\fR.
For \fBx\fR or \fBX\fR conversions, \fB0x\fR or \fB0X\fR (respectively)
will be added to the beginning of the result unless it is zero.
For \fBb\fR conversions, \fB0b\fR
will be added to the beginning of the result unless it is zero.
For all floating-point conversions (\fBe\fR, \fBE\fR, \fBf\fR,
\fBg\fR, and \fBG\fR) it guarantees that the result always

Convert integer to unsigned hexadecimal string, using digits
.QW 0123456789abcdef
for \fBx\fR and
.QW 0123456789ABCDEF
for \fBX\fR).
.TP 10
\fBb\fR
Convert integer to binary string, using digits 0 and 1.
.TP 10
\fBc\fR
Convert integer to the Unicode character it represents.
.TP 10
\fBs\fR
No conversion; just insert string.
.TP 10

'\"
'\" Copyright (c) 1995-1997 Sun Microsystems, Inc.
'\" Copyright (c) 1998-2000 by Ajuba Solutions.
'\" Copyright (c) 2004 ActiveState Corporation.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH "http" n 2.7 http "Tcl Bundled Packages"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
http \- Client-side implementation of the HTTP/1.1 protocol
.SH SYNOPSIS
\fBpackage require http ?2.7?\fR
.\" See Also -useragent option documentation in body!
.sp
\fB::http::config ?\fI\-option value\fR ...?
.sp
\fB::http::geturl \fIurl\fR ?\fI\-option value\fR ...?
.sp
\fB::http::formatQuery\fR \fIkey value\fR ?\fIkey value\fR ...?


.sp
\fB::http::reset\fR \fItoken\fR ?\fIwhy\fR?
.sp
\fB::http::wait \fItoken\fR
.sp
\fB::http::status \fItoken\fR
.sp

.sp
\fB::http::error \fItoken\fR
.sp
\fB::http::cleanup \fItoken\fR
.sp
\fB::http::register \fIproto port command\fR
.sp


\fB::http::unregister \fIproto\fR
.BE
.SH DESCRIPTION
.PP
The \fBhttp\fR package provides the client side of the HTTP/1.1
protocol, as defined in RFC 2616.
The package implements the GET, POST, and HEAD operations
of HTTP/1.1.  It allows configuration of a proxy host to get through
firewalls.  The package is compatible with the \fBSafesock\fR security
policy, so it can be used by untrusted applets to do URL fetching from
a restricted set of hosts. This package can be extended to support
additional HTTP transport protocols, such as HTTPS, by providing
a custom \fBsocket\fR command, via \fB::http::register\fR.

\fB\-accept\fR \fImimetypes\fR
.
The Accept header of the request.  The default is */*, which means that
all types of documents are accepted.  Otherwise you can supply a
comma-separated list of mime type patterns that you are
willing to receive.  For example,
.QW "image/gif, image/jpeg, text/*" .













.TP
\fB\-proxyhost\fR \fIhostname\fR
.
The name of the proxy host, if any.  If this value is the
empty string, the URL host is contacted directly.
.TP
\fB\-proxyport\fR \fInumber\fR

to determine if a proxy is required for a given host.  One argument, a
host name, is added to \fIcommand\fR when it is invoked.  If a proxy
is required, the callback should return a two-element list containing
the proxy server and proxy port.  Otherwise the filter should return
an empty list.  The default filter returns the values of the
\fB\-proxyhost\fR and \fB\-proxyport\fR settings if they are
non-empty.












.TP
\fB\-urlencoding\fR \fIencoding\fR
.
The \fIencoding\fR used for creating the x-url-encoded URLs with

\fB::http::formatQuery\fR.  The default is \fButf-8\fR, as specified by RFC
2718.  Prior to http 2.5 this was unspecified, and that behavior can be
returned by specifying the empty string (\fB{}\fR), although
\fIiso8859-1\fR is recommended to restore similar behavior but without the
\fB::http::formatQuery\fR throwing an error processing non-latin-1
characters.
.TP
\fB\-useragent\fR \fIstring\fR
.
The value of the User-Agent header in the HTTP request.  The default is










.QW "\fBTcl http client package 2.7\fR" .




.RE
.TP
\fB::http::geturl\fR \fIurl\fR ?\fIoptions\fR?
.
The \fB::http::geturl\fR command is the main procedure in the package.
The \fB\-query\fR option causes a POST operation and
the \fB\-validate\fR option causes a HEAD operation;

.CS
Pragma: no-cache
.CE
.RE
.TP
\fB\-keepalive\fR \fIboolean\fR
.
If true, attempt to keep the connection open for servicing
multiple requests.  Default is 0.
.TP
\fB\-method\fR \fItype\fR
.
Force the HTTP request method to \fItype\fR. \fB::http::geturl\fR will
auto-select GET, POST or HEAD based on other options, but this option
enables choices like PUT and DELETE for webdav support.

\fB::http::formatQuery\fR \fIkey value\fR ?\fIkey value\fR ...?
.
This procedure does x-url-encoding of query data.  It takes an even
number of arguments that are the keys and values of the query.  It
encodes the keys and values, and generates one string that has the
proper & and = separators.  The result is suitable for the
\fB\-query\fR value passed to \fB::http::geturl\fR.





.TP
\fB::http::reset\fR \fItoken\fR ?\fIwhy\fR?
.
This command resets the HTTP transaction identified by \fItoken\fR, if any.
This sets the \fBstate(status)\fR value to \fIwhy\fR, which defaults to
\fBreset\fR, and then calls the registered \fB\-command\fR callback.
.TP

package require tls

::http::register https 443 ::tls::socket

set token [::http::geturl https://my.secure.site/]
.CE
.RE











.TP
\fB::http::unregister\fR \fIproto\fR
.
This procedure unregisters a protocol handler that was previously
registered via \fB::http::register\fR, returning a two-item list of
the default port and handler command that was previously installed
(via \fB::http::register\fR) if there was such a handler, and an error if

Once the data associated with the URL is no longer needed, the state
array should be unset to free up storage.
The \fB::http::cleanup\fR procedure is provided for that purpose.
The following elements of
the array are supported:
.RS
.TP








\fBbody\fR
.
The contents of the URL.  This will be empty if the \fB\-channel\fR
option has been specified.  This value is returned by the \fB::http::data\fR command.
.TP
\fBcharset\fR
.

.
A copy of the \fBContent-Type\fR meta-data value.
.TP
\fBurl\fR
.
The requested URL.
.RE




































































































.SH EXAMPLE
.PP
This example creates a procedure to copy a URL to a file while printing a
progress meter, and prints the meta-data associated with the URL.
.PP
.CS
proc httpcopy { url file {chunk 4096} } {