{ "hex",      BinaryDecodeHex, TclCompileBasic1Or2ArgCmd, NULL, NULL, 0 },
    { "uuencode", BinaryDecodeUu,  TclCompileBasic1Or2ArgCmd, NULL, NULL, 0 },
    { "base64",   BinaryDecode64,  TclCompileBasic1Or2ArgCmd, NULL, NULL, 0 },
    { NULL, NULL, NULL, NULL, NULL, 0 }
};

/*
 * The following object types represent an array of bytes. The intent is
 * to allow arbitrary binary data to pass through Tcl as a Tcl value
 * without loss or damage. Such values are useful for things like
 * encoded strings or Tk images to name just two.
 *
 * It's strange to have two Tcl_ObjTypes in place for this task when
 * one would do, so a bit of detail and history how we got to this point
 * and where we might go from here.
 *
 * A bytearray is an ordered sequence of bytes. Each byte is an integer
 * value in the range [0-255].  To be a Tcl value type, we need a way to
 * encode each value in the value set as a Tcl string.  The simplest
 * encoding is to represent each byte value as the same codepoint value.
 * A bytearray of N bytes is encoded into a Tcl string of N characters




 * where the codepoint of each character is the value of corresponding byte.
 * This approach creates a one-to-one map between all bytearray values
 * and a subset of Tcl string values.
 * 
 * When converting a Tcl string value to the bytearray internal rep, the
 * question arises what to do with strings outside that subset?  That is,
 * those Tcl strings containing at least one codepoint greater than 255?
 * The obviously correct answer is to raise an error!  That string value
 * does not represent any valid bytearray value. Full Stop.  The
 * setFromAnyProc signature has a completion code return value for just
 * this reason, to reject invalid inputs.
 * 
 * Unfortunately this was not the path taken by the authors of the
 * original tclByteArrayType.  They chose to accept all Tcl string values
 * as acceptable string encodings of the bytearray values that result
 * from masking away the high bits of any codepoint value at all. This
 * meant that every bytearray value had multiple accepted string
 * representations.
 *
 * The implications of this choice are truly ugly.  When a Tcl value has
 * a string representation, we are required to accept that as the true
 * value.  Bytearray values that possess a string representation cannot
 * be processed as bytearrays because we cannot know which true value
 * that bytearray represents.  The consequence is that we drag around
 * an internal rep that we cannot make any use of.  This painful price
 * is extracted at any point after a string rep happens to be generated
 * for the value.  This happens even when the troublesome codepoints
 * outside the byte range never show up.  This happens rather routinely
 * in normal Tcl operations unless we burden the script writer with the
 * cognitive burden of avoiding it.  The price is also paid by callers

 * of the C interface.  The routine
 *
 *	unsigned char *Tcl_GetByteArrayFromObj(objPtr, lenPtr)
 *
 * has a guarantee to always return a non-NULL value, but that value
 * points to a byte sequence that cannot be used by the caller to  
 * process the Tcl value absent some sideband testing that objPtr
 * is "pure".  Tcl offers no public interface to perform this test,
 * so callers either break encapsulation or are unavoidably buggy.  Tcl
 * has defined a public interface that cannot be used correctly. The
 * Tcl source code itself suffers the same problem, and has been buggy,
 * but progressively less so as more and more portions of the code have
 * been retrofitted with the required "purity testing".  The set of values
 * able to pass the purity test can be increased via the introduction of
 * a "canonical" flag marker, but the only way the broken interface itself
 * can be discarded is to start over and define the Tcl_ObjType properly.
 * Bytearrays should simply be usable as bytearrays without a kabuki
 * dance of testing.
 *
 * The Tcl_ObjType "properByteArrayType" is (nearly) a correct 
 * implementation of bytearrays.  Any Tcl value with the type
 * properByteArrayType can have its bytearray value fetched and
 * used with confidence that acting on that value is equivalent to
 * acting on the true Tcl string value.  This still implies a side
 * testing burden -- past mistakes will not let us avoid that
 * immediately, but it is at least a conventional test of type, and
 * can be implemented entirely by examining the objPtr fields, with
 * no need to query the intrep, as a canonical flag would require.
 *
 * Until Tcl_GetByteArrayFromObj() and Tcl_SetByteArrayLength() can
 * be revised to admit the possibility of returning NULL when the true
 * value is not a valid bytearray, we need a mechanism to retain
 * compatibility with the deployed callers of the broken interface.
 * That's what the retained "tclByteArrayType" provides.  In those
 * unusual circumstances where we convert an invalid bytearray value
 * to a bytearray type, it is to this legacy type.  Essentially any
 * time this legacy type gets used, it's a signal of a bug being ignored.
 * A TIP should be drafted to remove this connection to the broken past
 * so that Tcl 9 will no longer have any trace of it.  Prescribing a
 * migration path will be the key element of that work.  The internal
 * changes now in place are the limit of what can be done short of
 * interface repair.  They provide a great expansion of the histories
 * over which bytearray values can be useful in the meanwhile.
 */

static const Tcl_ObjType properByteArrayType = {
    "bytearray",
    FreeByteArrayInternalRep,
    DupByteArrayInternalRep,
    UpdateStringOfByteArray,
    NULL
};

const Tcl_ObjType tclByteArrayType = {
    "bytearray",
    FreeByteArrayInternalRep,
    DupByteArrayInternalRep,
    NULL,
    SetByteArrayFromAny
};

/*
 * The following structure is the internal rep for a ByteArray object. Keeps
 * track of how much memory has been used and how much has been allocated for
 * the byte array to enable growing and shrinking of the ByteArray object with

#define BYTEARRAY_SIZE(len) \
		((TclOffset(ByteArray, bytes) + (len)))
#define GET_BYTEARRAY(objPtr) \
		((ByteArray *) (objPtr)->internalRep.twoPtrValue.ptr1)
#define SET_BYTEARRAY(objPtr, baPtr) \
		(objPtr)->internalRep.twoPtrValue.ptr1 = (void *) (baPtr)

int
TclIsPureByteArray(
    Tcl_Obj * objPtr)
{
    return (objPtr->typePtr == &properByteArrayType);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_NewByteArrayObj --
 *
 *	This procedure is creates a new ByteArray object and initializes it

    byteArrayPtr = ckalloc(BYTEARRAY_SIZE(length));
    byteArrayPtr->used = length;
    byteArrayPtr->allocated = length;

    if ((bytes != NULL) && (length > 0)) {
	memcpy(byteArrayPtr->bytes, bytes, (size_t) length);
    }
    objPtr->typePtr = &properByteArrayType;
    SET_BYTEARRAY(objPtr, byteArrayPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetByteArrayFromObj --

Tcl_GetByteArrayFromObj(
    Tcl_Obj *objPtr,		/* The ByteArray object. */
    int *lengthPtr)		/* If non-NULL, filled with length of the
				 * array of bytes in the ByteArray object. */
{
    ByteArray *baPtr;

    if ((objPtr->typePtr != &properByteArrayType)
	    && (objPtr->typePtr != &tclByteArrayType)) {
	SetByteArrayFromAny(NULL, objPtr);
    }
    baPtr = GET_BYTEARRAY(objPtr);

    if (lengthPtr != NULL) {
	*lengthPtr = baPtr->used;
    }

    size_t length)			/* New length for internal byte array. */
{
    ByteArray *byteArrayPtr;

    if (Tcl_IsShared(objPtr)) {
	Tcl_Panic("%s called with shared object", "Tcl_SetByteArrayLength");
    }
    if ((objPtr->typePtr != &properByteArrayType)
	    && (objPtr->typePtr != &tclByteArrayType)) {
	SetByteArrayFromAny(NULL, objPtr);
    }

    byteArrayPtr = GET_BYTEARRAY(objPtr);
    if (length > byteArrayPtr->allocated) {
	byteArrayPtr = ckrealloc(byteArrayPtr, BYTEARRAY_SIZE(length));
	byteArrayPtr->allocated = length;

static int
SetByteArrayFromAny(
    Tcl_Interp *interp,		/* Not used. */
    Tcl_Obj *objPtr)		/* The object to convert to type ByteArray. */
{
    size_t length;
    int improper = 0;
    const char *src, *srcEnd;
    unsigned char *dst;
    ByteArray *byteArrayPtr;
    Tcl_UniChar ch;

    if (objPtr->typePtr == &properByteArrayType) {
	return TCL_OK;
    }
    if (objPtr->typePtr == &tclByteArrayType) {
	return TCL_OK;
    }

    src = TclGetString(objPtr);
    length = objPtr->length;
    srcEnd = src + length;

    byteArrayPtr = ckalloc(BYTEARRAY_SIZE(length));
    for (dst = byteArrayPtr->bytes; src < srcEnd; ) {
	src += Tcl_UtfToUniChar(src, &ch);
	improper = improper || (ch > 255);
	*dst++ = UCHAR(ch);
    }

    byteArrayPtr->used = dst - byteArrayPtr->bytes;
    byteArrayPtr->allocated = length;

    TclFreeIntRep(objPtr);
    objPtr->typePtr = improper ? &tclByteArrayType : &properByteArrayType;
    SET_BYTEARRAY(objPtr, byteArrayPtr);

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * FreeByteArrayInternalRep --

    copyArrayPtr = ckalloc(BYTEARRAY_SIZE(length));
    copyArrayPtr->used = length;
    copyArrayPtr->allocated = length;
    memcpy(copyArrayPtr->bytes, srcArrayPtr->bytes, length);
    SET_BYTEARRAY(copyPtr, copyArrayPtr);

    copyPtr->typePtr = srcPtr->typePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * UpdateStringOfByteArray --
 *

    size = length;
    for (i = 0; (i < length) && (size != (size_t)-1); i++) {
	if ((src[i] == 0) || (src[i] > 127)) {
	    size++;
	}
    }
    if (size == (size_t)-1) {
	Tcl_Panic("max size for a Tcl value exceeded");
    }

    dst = ckalloc(size + 1);
    objPtr->bytes = dst;
    objPtr->length = size;

    if (size == length) {

	Tcl_Panic("%s must be called with definite number of bytes to append",
		"TclAppendBytesToByteArray");
    }
    if (len == 0) {
	/* Append zero bytes is a no-op. */
	return;
    }
    if ((objPtr->typePtr != &properByteArrayType)
	    && (objPtr->typePtr != &tclByteArrayType)) {
	SetByteArrayFromAny(NULL, objPtr);
    }
    byteArrayPtr = GET_BYTEARRAY(objPtr);

    if (len + byteArrayPtr->used > UINT_MAX) {
	Tcl_Panic("max size for a Tcl value (%u bytes) exceeded", UINT_MAX);
    }