 NAME
 OVERVIEW
 DOWNLOAD
 INSTALLATION
 IMPLEMENTATION
 EXAMPLES
 VERIFICATION TESTS
 REFERENCE
 Decimal Numbers
 Decimal Contexts
 Random States
 Constants
 Rounding
 Status Flags
 Classifications
 Initialization Descriptors
 Compile time configuration
 Operations on Contexts
decNumber.getcontext
decctx:duplicate
decctx:setcontext
decctx:setdefault
decctx:getclamp
decctx:getdigits
decctx:getemax
decctx:getemin
decctx:getround
decctx:getstatus
decctx:getstatusstring
decctx:gettraps
decctx:setclamp
decctx:setdigits
decctx:setemax
decctx:setemin
decctx:setround
decctx:setstatus
decctx:setstatusstring
decctx:settraps
 Operations on Numbers
decnum:__concat
decnum:toengstring
decNumber.tonumber
decnum:tostring
decnum:abs
decnum:add
decnum:copy
decnum:copyabs
decnum:copynegate
decnum:copysign
decnum:divide
decnum:divideinteger
decnum:exp
decnum:floor
decnum:fma
decnum:invert
decnum:land
decnum:ln
decnum:log10
decnum:logb
decnum:lor
decnum:max
decnum:maxmag
decnum:min
decnum:minmag
decnum:minus
decnum:mod
decnum:multiply
decnum:nextminus
decnum:nextplus
decnum:nexttoward
decnum:normalize
decnum:plus
decnum:power
decnum:quantize
decnum:remainder
decnum:remaindernear
decnum:rescale
decnum:rotate
decnum:samequantum
decnum:scaleb
decnum:shift
decnum:squareroot
decnum:subtract
decnum:tointegralexact
decnum:tointegralvalue
decnum:trim
decnum:xor
decnum:class
decnum:classasstring
classtostring
decnum:compare
decnum:comparetotal
decnum:comparetotalmag
decnum:eq
decnum:iscanonical
decnum:isfinite
decnum:isinfinite
decnum:isnan
decnum:isnegative
decnum:isnormal
decnum:isqnan
decnum:issnan
decnum:isspecial
decnum:issubnormal
decnum:iszero
decnum:le
decnum:lt
decnum:radix
 Operations on Random States
 VERSION
 CREDITS
 LICENSE
NAME
ldecNumber  a Lua 5.1 wrapper for the Decimal Number library decNumber
OVERVIEW
The ldecNumber package is a Lua module for General Decimal Arithmetic. For the background and rationale for the design of the arithmetic, see Decimal FloatingPoint: Algorism for Computers in the Proceedings of the 16th IEEE Symposium on Computer Arithmetic (Cowlishaw, M. F., 2003). http://www2.hursley.ibm.com/decimal/IEEEcowlishawarith16.pdf The decNumber package, an arbitraryprecision implementation of the specifications in ANSI C, provides a reference implementation for both the arithmetic and the encodings, and is used as the basis for the ldecNumber package. See Mike Cowlishaw's decimal page http://www2.hursley.ibm.com/decimal/ for more information and the latest versions of the decNumber package and test code.
The ldecNumber package was designed to provide the arithmetic facilities of the decNumber package with a Lua flavor. It is a loadable Lua module, designed for Lua 5.1.
DOWNLOAD
ldecNumber source code can be downloaded from its LuaForge (http://luaforge.net/projects/ldecnumber/) page.
The source code from the decNumber package and the decTest package are included in the ldecNumber distribution for a few reasons:

A couple of minor modifications were made to decTest to correct syntax errors.

The decNumber package is fairly small, and including it is a convenience to users as well as a means of documenting exactly the code used to build and test the ldecNumber package

IBM's liberal ICU License allows me to do so!
The distribution also includes a copy of the decNumber C library
User's Guide, decNumber.pdf. This is the best reference for the
specification of most of the functions included in the decNumber
module.
INSTALLATION
A Makefile is provided.
IMPLEMENTATION
A few arbitrary choices were made in the implementation of the Lua wrapper.
Precision
The size of structures used in the decNumber package determines the
maximum number of decimal digits in decimal numbers it can manipulate.
The default build of the decNumber
module is configured for 69 digits.
This number was chosen for a couple reasons: the resulting structure
size is between 57 and 64 bytes in size (so each decimal number takes
this this much space), and this precision is a bit more than twice
what is needed for Decimal128 external format. Providing twice the
external format's precision seemed like a good practice for mitigation
of rounding issues during calculations with these numbers.
Note: the ldecNumber package does not yet support any external binary formats, such as Decimal128, though it may in the future. Presently Lua strings and Lua numbers are the only "external" formats.
In any case, you may change the value of DECNUMDIGITS
during a build
of the decNumber
module to accommodate more digits, or reduce memory
overhead if you need fewer digits. The decNumber
module has only been
tested with the default setting, and one or two others.
Context
The decNumber context provides configuration settings such as working precision and rounding mode, and also holds condition flags. Functions in the decNumber package take a context argument. Using this approach in Lua would have made infix operator syntax impossible. This would not have been very Lualike.
Instead, the decNumber
module automatically maintains a decNumber
context per Lua thread. This thread decNumber context may be modified
and inspected. It may also be retrieved and restored, so threads may
maintain multiple contexts if desired. Modifications to the context
in one thread do not affect the contexts in other threads, unless, of
course, threads explicitly retrieve, exchange, and replace their
contexts with a shared context. (If you don't use setcontext you
don't need to worry!)
The default decNumber context is DEC_INIT_DECIMAL128
as described
in decNumber.pdf. This default may be changed during a build of the
decNumber
module by changing the value of LDN_CONTEXT_DEFAULT
.
The context method setdefault may be used to initialize a context to
one of the well known default configurations.
Naming Convention
Names in the decNumber package follow a convention of a
decNumber
or DEC_
prefix and mixed case, or for some constants,
upper case. Lua code, on the other hand, tends toward lower case
identifiers. I attempted to unify this by

using
decNumber
as the module name 
stripping the prefix described above from the function names and constants (since the module name prefix will typically be there anyway)

using lower case for function names, but otherwise retaining the spelling, and

retaining the case for constant names
There are two cases where in following these rules the decNumber
names clash with Lua reserved words or
and and
 in these
cases the decNumber functions are called "logical" operations,
so I called the functions lor
and land
.
Wherever there was a predefined Lua metamethod, e. g., __add
, the
appropriate function is bound to that name as well as the decNumber
package function name.
Where it seemed appropriate, functions are provided both as methods
on decimal numbers, as well as functions in the decNumber
module.
Mutability
The decimal numbers created by Lua are not mutable. This decision was based on my judgment that the potential performance benefit, mainly lower memory consumption and less garbage collection, was outweighed by the safety and lack of "surprise" that immutability provides. This makes decimal numbers compatible with Lua numbers and strings, both of which are also not mutable.
Conversion
All the functions in the decNumber
module automatically convert
their arguments from Lua numbers or strings as necessary to perform
the operation. This conversion is done with the current settings in
the thread decNumber context.
EXAMPLES
The distribution contains an examples directory with Lua translations of some of the C examples from the decNumber package.
VERIFICATION TESTS
The distribution contains a test directory with a few test files.
Unit Tests
File: ldecNumberUnitTest.lua
This is a small but expanding set of unit tests for the decNumber
module. It uses the lunit module that can be obtained from Mike
Roth's page http://www.nessie.de/mroth/lunit/.
File: ldecNumberGausstest.lua
This is a small small tests for the
decNumber.randomstate
function and use of Random States. It defines a Gaussian random
number generator, and tests it by graphing the result of many
executions. It uses the Lua DISLIN library for graphing, see
LuaForge for Lua DISLIN
http://luaforge.net/projects/ldislin/files.
File: ldecNumberThreadsTest.lua
This is a simple test that the decimal context in each thread is independent. It requires visual inspection of the results to verify that thread 1 is rounding ROUND_HALF_DOWN and thread 2 is rounding ROUND_HALF_EVEN.
Performance Tests
File: ldecNumberPerf.lua
This is a simple test of the speed of some arbitrary decNumber
module functions. It was useful to confirm that decimal context
caching was worthwhile. It relies on the lperformance module, which
is included, but has been designed for WindowsXP.
Compliance Test
File: ldecNumberTestDriver.lua
This is the big test. It uses dectest sources from IBM, and has over 60,000 test cases. The Lua file is a driver to execute the tests specified by dectest.
As of version 21 of the Lua decNumber
module, the results for this
test (dectest version 2.55) are:
For all 60937 tests, 59951 succeeded, 5 failed, 301 failed(conv), 644 skipped(#), 36 skipped(prec).
This is as good as possible with the default configuration. What this means is:
59951 succeeded woot! 5 failed these 5 tests are know to fail in the decNumber C library; these edge cases are under reconsideration in the Decimal Number Specification 301 failed(conv) the precision required for the operands is insufficient in the Lua wrapper 644 skipped(#) the test is for NULL arguments or format conversions not supported 36 skipped(prec) the test called for a precision larger than provided in the Lua wrapper
REFERENCE
Here is a reference to the data types, constants, and functions in the
decNumber
module. Many of these will refer to the decNumber C library
User's Guide, decNumber.pdf, for implementation details.
The decNumber
module defines three userdata types with their own
metatables. These are Decimal Numbers, Decimal Contexts, and
decimal Random States.
Decimal Numbers
Decimal numbers are immutable numeric values. In the default configuration they can have up to 69 digits of precision, and exponents of 999999999 to 999999999.
Decimal numbers are created by the functions in the decNumber
module. Since any arguments to these functions may be strings,
Lua numbers, or decimal numbers, conversion from strings or
Lua numbers to decimal numbers can be achieved in may ways.
The function decNumber.tonumber
is
the most obvious.
In the descriptions below, arguments or results that may be a
string, Lua number, or decimal number are indicated by <decarg>
whereas arguments or results that must be a decimal number
are indicated by decnum
.
The metatable for decimal numbers is available as
decNumber.number_metatable
.
Decimal Contexts
Decimal contexts are mutable records that contain

flags that control behaviors of the
decNumber
module, such as precision and rounding 
conditions that report the status of sequence of operations, such as overflow
See Context for some rational on how the decNumber
module manages contexts.
In the descriptions below, arguments or results that must be a
decimal context are indicated by decctx
.
The metatable for decimal contexts is available as
decNumber.context_metatable
.
Random States
Random states are mutable records that contain opaque data for generation of random numbers.
See Operations on Random States for the description of functions for creating and using random states.
In the descriptions below, arguments or results that must be a
decimal context are indicated by decrst
.
The metatable for decimal contexts is available as
decNumber.drandom_metatable
.
Constants
Here are the constants exposed in the decNumber
module from the
decNumber package.
Rounding
These numeric flags are used with
decctx:setround(x)
decNumber.ROUND_CEILING round towards +infinity decNumber.ROUND_UP round away from 0 decNumber.ROUND_HALF_UP 0.5 rounds up decNumber.ROUND_HALF_EVEN 0.5 rounds to nearest even decNumber.ROUND_HALF_DOWN 0.5 rounds down decNumber.ROUND_DOWN round towards 0 (truncate) decNumber.ROUND_FLOOR round towards infinity decNumber.ROUND_05UP round for reround
Status Flags
These numeric status flags are used with
decctx:getstatus()
decNumber.Conversion_syntax decNumber.Division_by_zero decNumber.Division_impossible decNumber.Division_undefined decNumber.Insufficient_storage decNumber.Inexact decNumber.Invalid_context decNumber.Invalid_operation decNumber.Overflow decNumber.Clamped decNumber.Rounded decNumber.Subnormal decNumber.Underflow
These constants are combinations of the above status flags:
decNumber.IEEE_854_Division_by_zero decNumber.IEEE_854_Inexact decNumber.IEEE_854_Invalid_operation decNumber.IEEE_854_Overflow decNumber.IEEE_854_Underflow decNumber.Errors normally errors (results are qNaN, infinite, or 0) decNumber.NaNs cause a result to become qNaN decNumber.Information normally for information only (have finite results)
Classifications
These numeric classifications for decNumbers are aligned with IEEE 754r
and are returned by
decnum:class()
Note that 'normal' and 'subnormal' are meaningful only with a decContext.
decNumber.CLASS_SNAN decNumber.CLASS_QNAN decNumber.CLASS_NEG_INF decNumber.CLASS_NEG_NORMAL decNumber.CLASS_NEG_SUBNORMAL decNumber.CLASS_NEG_ZERO decNumber.CLASS_POS_ZERO decNumber.CLASS_POS_SUBNORMAL decNumber.CLASS_POS_NORMAL decNumber.CLASS_POS_INF
These classifications are also returned as string values from
decnum:classasstring()
Initialization Descriptors
These constants are used with
decctx:setdefault(x)
decNumber.INIT_BASE decNumber.INIT_DECIMAL32 decNumber.INIT_DECIMAL64 decNumber.INIT_DECIMAL128
See note re: decNumber.INIT_BASE
and traps, below in
decctx:setdefault(x)
Compile time configuration
These constants provide information about the compile time configuration.
decNumber.MAX_DIGITS constant DECNUMDIGITS, the maximum precision
decNumber.version a string with the decNumber module version information
Operations on Contexts
The following functions operate on decimal contexts. See the decNumber C library User's Guide, decNumber.pdf for details about contexts, and constants used for manipulating them.
decNumber.getcontext
decNumber.getcontext ()
Returns the thread's current decimal context.
decctx:duplicate
decctx:duplicate()
Returns a copy of the decimal context argument. This may be used, for example, to save and restore a context around temporary modifications, or to keep multiple decimal contexts on hand for quick wholesale context changes (rather than changing individual fields). You probably don't ever need to do this!
decctx:setcontext
decNumber.setcontext (decctx) decctx:setcontext ()
Sets the thread's decimal context to the argument, and returns the previous decimal context, i. e., the one that was just replaced. You probably don't ever need to do this!
decctx:setdefault
decctx:setdefault (initconst)
Initializes the context argument to the settings specified by the initconst. See Initialization Descriptors for permitted values for initconst. No values are returned.
Note: since traps are not supported, decNumber.INIT_BASE
differs
from the behavior documented in the decNumber C library User Guide in
that it leaves traps disabled.
Uses the C library function decContextDefault()
.
decctx:getclamp
decctx:getclamp ()
Returns the integer value of the clamp
field of the context
argument. When 0, a result exponent is limited to emax
(for
example, the exponent of a zero result will be clamped to this value).
When 1, a result exponent is limited to emax(digits1)
.
decctx:getdigits
decctx:getdigits ()
Returns the integer value of the digits
field of the context
argument. This is the working precision for this decimal context.
The results of decimal number operations will be rounded to this
length if necessary.
decctx:getemax
decctx:getemax ()
Returns the integer value of the emax
field of the context
argument. This is the magnitude of the largest adjusted exponent
that is permitted.
decctx:getemin
decctx:getemin ()
Returns the integer value of the emin
field of the context
argument. This is the smallest adjusted exponent that is permitted
for normal numbers.
decctx:getround
decctx:getround ()
Returns the integer value of the round
field of the context
argument. See Rounding for possible values.
decctx:getstatus
decctx:getstatus ()
Returns the integer value of the status
field of the context
argument. See Status Flags for possible values. In general,
the result will be a bitwiseor of a subset of these values.
decctx:getstatusstring
decctx:getstatusstring ()
Returns a string derived from the present value of the context
argument's status field using the C library function
decContextStatusToString()
.
decctx:gettraps
decctx:gettraps ()
Returns 0 (we hope!) since traps are not implemented in the Lua wrapper  use the status flags instead!
decctx:setclamp
decctx:setclamp (num)
Sets the integer value of the clamp
field of the context
argument to num
. When 0, a result exponent is limited to
emax
(for example, the exponent of a zero result will be
clamped to this value). When 1, a result exponent is limited
to emax  (digits  1)
.
Returns the previous value of the clamp
field.
Note that it is an error if num is not one of the values 0 or 1.
decctx:setdigits
decctx:setdigits (num)
Sets the integer value of the digits
field of the context
argument to num
. This is the working precision for this
decimal context. The results of subsequent decimal number
operations will be rounded to this length if necessary.
Returns the previous value of the digits
field.
Note that it is an error if num exceeds decNumber.MAX_DIGITS
.
decctx:setemax
decctx:setemax (num)
Sets the integer value of the emax
field of the context
argument to num
. This is the magnitude of the largest
adjusted exponent that is permitted.
Returns the previous value of the emax
field.
Note that it is an error if num is outside the range 0 though 999,999,999.
decctx:setemin
decctx:setemin (num)
Sets the integer value of the emin
field of the context
argument to num
. This is the smallest adjusted exponent
that is permitted for normal numbers. emin
will usually equal
emax
, but when a compressed format is used it will be
(emax1)
.
Returns the previous value of the emin
field.
Note that it is an error if num is outside the range 999,999,999 though 0.
decctx:setround
decctx:setround (rounding)
Sets the integer value of the round
field of the context
argument to rounding
. This is used to select the rounding
algorithm to be used if rounding is necessary during subsequent
decimal number operations.
Returns the previous value of the round
field.
Note that it is an error if rounding is not one of the values described in Rounding.
decctx:setstatus
decctx:setstatus (flags)
Sets the integer value of the status
field of the context
argument to flags
. See Status Flags for possible values.
In general, the flags will be a bitwiseor of a subset of these
values. Usually the flags
are 0 to clear all conditions.
Returns the previous value of the status field.
Note that it is an error if flags is not a bitwiseor of a subset of the values in Status Flags.
decctx:setstatusstring
decctx:setstatusstring (flagname)
Sets the decimal context's status bit corresponding to the name
string argument flagname
using the C library function
decContextSetStatusFromString()
.
decctx:settraps
decctx:settraps (flags)
Sets the integer value of the traps
field of the context
argument to flags
.
Note that it is an error if flags
is not zero since traps
are not implemented in the Lua wrapper  use the status
flags instead!
Operations on Numbers
The following functions operate on decimal numbers. In the
descriptions below, arguments or results that may be a string,
Lua number, or decimal number are indicated by decarg
whereas
arguments or results that must be a decimal number are indicated by
decnum
. See Decimal Numbers.
See the decNumber C library User's Guide, decNumber.pdf for details about limitations of the functions, and behavior in exceptional situations.
Conversions
decnum:__concat
decnum:__concat (<string>)
Returns a string representing the value of the decimal number
argument concatenated with the string argument. See
decnum:tostring
below for a description
of the conversion operation.
Note that by binding the method __concat to this function, the
Lua ..
concatenation operator will work with a decimal number
and a string, in either order, due to Lua's internal application
of this method when one side of the ..
concatenation operator
is a decimal number.
Uses the C library function decNumberToString()
.
decnum:toengstring
decnum:toengstring () decNumber.toengstring (decarg)
Returns a string representing the value of the argument (converted to a decimal number first if necessary) using engineering notation (where the exponent will be a multiple of three, and there may be up to three digits before any decimal point) if an exponent is needed. It implements the toengineeringstring conversion.
Uses the C library function decNumberToEngString()
.
decNumber.tonumber
decNumber.tonumber (decarg)
Returns a decimal number. If the argument is a decimal number, it is simply returned. If the argument is a Lua number or string, it is converted, using the present decimal context as usual, to a decimal number and this value is returned.
Uses the C library function decNumberFromString()
.
decnum:tostring
decnum:tostring () decnum:__tostring () decNumber.tostring (decarg)
Returns a string representing the value of the argument (converted to a decimal number first if necessary) using scientific notation if an exponent is needed (that is, there will be just one digit before any decimal point). It implements the toscientificstring conversion.
Note that by binding the method __tostring
to this function, the
Lua print
and tostring
functions will work with decimal numbers,
using this conversion function.
Uses the C library function decNumberToString()
.
Operations
decnum:abs
decnum:abs () decNumber.abs (decarg)
Returns a decimal number that is the absolute value of the argument.
Uses the C library function decNumberAbs()
.
decnum:add
decnum:add (decarg) decnum:__add (decarg) decNumber.add (decarg, decarg)
Returns a decimal number that is the sum of its arguments.
Note that by binding the method __add
to this function, the
Lua addition operator (+
) may be used with a decnum
on the
left and a decarg
on the right.
Uses the C library function decNumberAdd()
.
decnum:copy
decnum:copy () decNumber.copy (decarg)
Returns a decimal number that is a copy of its argument. This is
not too useful since decnum
s are immutable in ldecNumber,
but it could be used as an alternative to
decnum:tonumber
No error is possible from this function when its argument is a
decnum
.
Uses the C library function decNumberCopy()
.
decnum:copyabs
decnum:copyabs () decNumber.copyabs (decarg)
Returns a decimal number that is the absolute value of its argument.
This is the quiet abs
function described in IEEE 754r.
No error is possible from this function when its argument is a
decnum
.
Uses the C library function decNumberCopyAbs()
.
decnum:copynegate
decnum:copynegate () decNumber.copynegate (decarg)
Returns a decimal number that is the negation of its argument, in
other words it returns a copy of its argument with the sign inverted.
This is the quiet negate
function described in IEEE 754r.
No error is possible from this function when its argument is a
decnum
.
Uses the C library function decNumberCopyNegate()
.
decnum:copysign
decnum:copysign (decarg) decNumber.copysign (decarg, decarg)
Returns a decimal number that is a copy of its first argument but
with the sign of its second argument.
This is the quiet copysign
function described in IEEE 754r.
No error is possible from this function when its arguments are
both decnum
s.
Uses the C library function decNumberCopySign()
.
decnum:divide
decnum:divide (decarg) decnum:__div (decarg) decNumber.divide (decarg, decarg)
Returns a decimal number that is the left (1st) argument divided by the right (2nd) argument.
Note that by binding the method __div
to this function, the
Lua division operator (/
) may be used with a decnum
on the
left and a decarg
on the right.
Uses the C library function decNumberDivide()
.
decnum:divideinteger
decnum:divideinteger (decarg) decNumber.divideinteger (decarg, decarg)
Returns a decimal number that is the integer part of the result
of dividing of its arguments. Note that, per the decNumber
specification, this is a convert to integer by truncation. If
you want some other rounding mode, use decnum:floor
,
or for any rounding mode use
decnum:tointegralvalue
or decnum:quantize
.
Uses the C library function decNumberDivideInteger()
.
decnum:exp
decnum:exp () decNumber.exp (decarg)
Returns a decimal number that is e raised to the power of the argument.
Uses the C library function decNumberExp()
.
decnum:floor
decnum:floor (decarg) decNumber.floor (decarg, decarg)
Returns a decimal number integer that is the floor of the left (1st)
argument divided by the right (2nd) argument. Contrast this with
decnum:divideinteger
which uses truncation.
The floor function is implemented as equal to
decnum:divideinteger
if the signs of the
arguments are the same or if the remainder is zero, otherwise as equal
to the decnum:divideinteger
result minus 1.
The current context's rounding mode is used.
See decnum:mod
.
Uses the C library function decNumberDivideInteger()
, and then
decNumberMultiply()
followed by decNumberCompare() decNumberIsZero()
to check if the remainder is zero, and decNumberSubtract()
.
decnum:fma
decnum:fma (decarg,decarg) decNumber.fma (decarg, decarg, decarg)
Returns a decimal number that is the result of multiplying the first argument by the second argument and then adding the third argument to that intermediate result. It is equivalent to a multiplication followed by an addition except that the intermediate result is not rounded and will not cause overflow or underflow. That is, only the final result is rounded and checked.
Uses the C library function decNumberFMA()
.
decnum:invert
decnum:invert () decNumber.invert (decarg)
Returns a decimal number that is the result of the digitwise logical inversion of the argument (a 0 digit becomes 1 and vice versa).
Uses the C library function decNumberInvert()
.
decnum:land
decnum:land (decarg) decNumber.land (decarg, decarg)
Returns a decimal number that is the digitwise logical and of the arguments. Note that all digits of the arguments must be 0 or 1 or else this operation returns NaN,
Uses the C library function decNumberAnd()
.
decnum:ln
decnum:ln () decNumber.ln (decarg)
Returns a decimal number that is the natural logarithm (logarithm in base e) of the argument.
Uses the C library function decNumberLn()
.
decnum:log10
decnum:log10 () decNumber.log10 (decarg)
Returns a decimal number that is the logarithm in base ten of the argument.
Uses the C library function decNumberLog10()
.
decnum:logb
decnum:logb () decNumber.logb (decarg)
Returns a decimal number that is the adjusted exponent of the
argument, according to the rules for the logB
operation of the
IEEE 754r proposal. This returns the exponent of the argument as
though its decimal point had been moved to follow the first digit
while keeping the same value. The result is not limited by
emin
or emax
.
Uses the C library function decNumberLogB()
.
decnum:lor
decnum:lor (decarg) decNumber.lor (decarg, decarg)
Returns a decimal number that is the digitwise logical inclusive or of the arguments. Note that all digits of the arguments must be 0 or 1 or else this operation returns NaN,
Uses the C library function decNumberOr()
.
decnum:max
decnum:max (decarg) decNumber.max (decarg, decarg)
Returns a decimal number that is the maximum of its arguments.
Uses the C library function decNumberMax()
.
decnum:maxmag
decnum:maxmag (decarg) decNumber.maxmag (decarg, decarg)
Returns a decimal number that is the one of its arguments that
has the maximum magnitude. It is identical to
decnum:max
except that the signs of the operands
are ignored and taken to be 0 (nonnegative).
Uses the C library function decNumberMaxMag()
.
decnum:min
decnum:min (decarg) decNumber.min (decarg, decarg)
Returns a decimal number that is the minimum of its arguments.
Uses the C library function decNumberMin()
.
decnum:minmag
decnum:minmag (decarg) decNumber.minmag (decarg, decarg)
Returns a decimal number that is the one of its arguments that
has the minimum magnitude. It is identical to
decnum:min
except that the signs of the operands
are ignored and taken to be 0 (nonnegative).
Uses the C library function decNumberMinMag()
.
decnum:minus
decnum:minus () decnum:__unm () decNumber.minus (decarg)
Returns a decimal number that is the result of subtracting the argument from 0.
Note that by binding the method __unm
to this function, the
Lua unary minus operator (
) may be used with decimal numbers.
Uses the C library function decNumberMinus()
.
decnum:mod
decnum:mod (decarg) decnum:__mod (decarg) decNumber.mod (decarg, decarg)
Returns a decimal number that is remainder of the left (1st)
argument divided by the right (2nd) argument based on Lua rules
for the mod operator (%
). Lua defines
a % b == a  floor(a/b)*b
whereas the General Decimal Arithmetic Specification defines remainder using truncation.
The mod
function is implemented as equal to
decnum:remainder
if the signs of the
arguments are the same or the remainder is zero, otherwise as
equal to the remainder plus the divisor. The current context's
rounding mode is used.
Note that by binding the method __mod
to this function, the
Lua modulo operator (%
) may be used with a decnum
on the
left and a decarg
on the right.
Uses the C library functions decNumberRemainder()
,
decNumberIsNegative()
, decNumberIsZero()
, and decNumberAdd()
.
decnum:multiply
decnum:multiply (decarg) decnum:__mul (decarg) decNumber.multiply (decarg, decarg)
Returns a decimal number that is the product of its arguments.
Note that by binding the method __mul
to this function, the Lua
multiplication operator (*
) may be used with a decnum
on the
left and a decarg
on the right.
Uses the C library function decNumberMultiply()
.
decnum:nextminus
decnum:nextminus () decNumber.nextminus (decarg)
Returns a decimal number that is the closest value to the argument
in the direction of Infinity. This is computed as though by
subtracting an infinitesimal amount from the argument
using ROUND_FLOOR
, except that no flags are set as long as the
argument is a decnum
(unless the argument is a signaling NaN).
This function is a generalization of the IEEE 754 nextDown
operation.
Uses the C library function decNumberNextMinus()
.
decnum:nextplus
decnum:nextplus () decNumber.nextplus (decarg)
Returns a decimal number that is the closest value to the argument
in the direction of +Infinity. This is computed as though by
adding an infinitesimal amount from the argument
using ROUND_CEILING
, except that no flags are set as long as the
argument is a decnum
(unless the argument is a signaling NaN).
This function is a generalization of the IEEE 754 nextUp
operation.
Uses the C library function decNumberNextPlus()
.
decnum:nexttoward
decnum:nexttoward (decarg) decNumber.nexttoward (decarg, decarg)
Returns a decimal number that is the closest value to the first
argument in the direction of the second argument. This is computed
as though by adding or subtracting an infinitesimal amount to the
first argument using either ROUND_CEILING
or ROUND_FLOOR
depending on whether the second argument is larger or smaller than
the first argument. If the arguments are numerically equal, then
the result is a copy of the first argument with the sign of the
second argument. Flags are set as usual for an addition or
subtraction (no flags are set in the equals case).
This function is a generalization of the IEEE 754 nextAfter
operation.
Uses the C library function decNumberNextToward()
.
decnum:normalize
decnum:normalize () decNumber.normalize (decarg)
Returns a decimal number that is the result of adding the argument to 0, and putting the result in its simplest form. That is, a nonzero number which has any trailing zeros in the coefficient has those zeros removed by dividing the coefficient by the appropriate power of ten and adjusting the exponent accordingly, and a zero has its exponent set to 0.
Uses the C library function decNumberNormalize()
.
decnum:plus
decnum:plus () decNumber.plus (decarg)
Returns a decimal number that is the result of adding the argument to 0. This takes place according to the settings given in the decimal context, following the usual arithmetic rules. This may therefore be used for rounding.
Uses the C library function decNumberPlus()
.
decnum:power
decnum:power (decarg) decnum:__pow (decarg) decNumber.power (decarg, decarg)
Returns a decimal number that is the left (1st) argument raised to the power of the right (2nd) argument.
Note that by binding the method __pow
to this function, the Lua
power operator (^
) may be used with a decnum
on the left
and a decarg
on the right.
Uses the C library function decNumberPower()
.
decnum:quantize
decnum:quantize (decarg) decNumber.quantize (decarg, decarg)
Returns a decimal number that is numerically equal (except for any rounding) to the left (1st) argument but modified so its exponent has a specific value, equal to that of the right (2nd) argument. To achieve this, the coefficient of the result is adjusted (by rounding or shifting) so that its exponent has the requested value. For example, if the left (1st) argument had the value 123.4567, and the right (2nd) argument had the value 0.12, the result would be 123.46 (that is, 12346 with an exponent of 2, matching the right (2nd) argument).
Uses the C library function decNumberQuantize()
.
decnum:remainder
decnum:remainder (decarg) decNumber.remainder (decarg, decarg)
Returns a decimal number that is the remainder of the left (1st) argument divided by the right (2nd) argument. The identity
lhs == (lhs:divideinteger(rhs) * rhs) + lhs:remainder(rhs)
holds.
Uses the C library function decNumberRemainder()
.
decnum:remaindernear
decnum:remaindernear (decarg) decNumber.remaindernear (decarg, decarg)
Returns a decimal number that is the remainder of the left (1st)
argument divided by the right (2nd) argument using the rules
defined in IEEE 854. This follows the same definition as
decnum:remainder
, except that the nearest
integer quotient (or the nearest even integer if the remainder
is equidistant from two) is used instead of the result from
decnum:divideinteger
.
For example, decNumber.remaindernear(10, 6)
has the result 2
(instead of 4) because the multiple of 6 nearest to 10 is 12
(rather than 6).
Uses the C library function decNumberRemainderNear()
.
decnum:rescale
decnum:rescale (decarg) decNumber.rescale (decarg, decarg)
Returns a decimal number that is numerically equal (except for
any rounding) to the left (1st) argument but modified so its exponent
has the value of the right (2nd) argument. See
decnum:quantize
.
The right (2nd) argument must be a whole number (before any rounding);
that is, any digits in the fractional part of the number must be zero.
Uses the C library function decNumberRescale()
.
decnum:rotate
decnum:rotate (decarg) decNumber.rotate (decarg, decarg)
Returns a decimal number that is the first argument with the digits of its coefficient rotated to the left (if the second argument is positive) or to the right (if the second argument is negative) without adjusting the exponent or the sign.
If the first argument has fewer digits than context digits
the
coefficient is padded with zeros on the left before the
rotate. Any leading zeros in the result are ignored, as usual.
The second argument is the count of digits to rotate; it must be an
integer (that is, it must have an exponent of 0) and must be in the
range digits
through +digits
in the current context.
Uses the C library function decNumberRotate()
.
decnum:samequantum
decnum:samequantum (decarg) decNumber.samequantum (decarg, decarg)
Returns the decimal number 1 when the exponents of the arguments are equal, or if they are both Infinities or they are both NaNs; in all other cases returns the decimal number 0. This function is used to test whether the exponents of two numbers are equal. The coefficients and signs of the arguments are ignored.
Uses the C library function decNumberSameQuantum()
.
decnum:scaleb
decnum:scaleb (decarg) decNumber.scaleb (decarg, decarg)
This function returns the result of multiplying the first argument by
ten raised to the power of the second argument. It is used to adjust
(scale) the exponent of a number, using the rules of the scaleB
operation in the IEEE 754r proposal. The second argument must be an
integer (that is, it must have an exponent of 0) and it must also be
in the range n
through +n
, where n
is
2 * (context.emax + context.digits)
.
Uses the C library function decNumberScaleB()
.
decnum:shift
decnum:shift (decarg) decNumber.shift (decarg, decarg)
Returns a decimal number that is the first argument with the digits of its coefficient shifted to the left (if the second argument is positive) or to the right (if the second argument is negative) without adjusting the exponent or the sign.
The coefficient is padded with zeros on the left or right, as necessary. Any leading zeros in the result are ignored, as usual.
The second argument is the count of digits to shift; it must be an
integer (that is, it must have an exponent of 0) and must be in the
range digits
through +digits
in the current context.
Uses the C library function decNumberShift()
.
decnum:squareroot
decnum:squareroot () decNumber.squareroot (decarg)
Returns a decimal number that is the square root of its argument, rounded if necessary using the digits setting in the decimal context and using the roundhalfeven rounding algorithm.
Uses the C library function decNumberSquareRoot()
.
decnum:subtract
decnum:subtract (decarg) decnum:__sub (decarg) decNumber.subtract (decarg, decarg)
Returns a decimal number that is the left (1st) argument minus the right (2nd) argument.
Note that by binding the method __sub
to this function, the Lua
subtraction operator (
) may be used with a decnum
on the left
and a decarg
on the right.
Uses the C library function decNumberSubtract()
.
decnum:tointegralexact
decnum:tointegralexact () decNumber.tointegralexact (decarg)
Returns a decimal number that is the argument with any fractional part removed, if necessary, using the rounding mode in the decimal context.
The Inexact
flag is set if the result is numerically different
from the argument. Other than that, no flags are set as long as the
argument is a decnum
(unless the argument is a signaling NaN).
The result may have a positive exponent.
Uses the C library function decNumberToIntegralExact()
.
decnum:tointegralvalue
decnum:tointegralvalue () decNumber.tointegralvalue (decarg)
Returns a decimal number that is the argument with any fractional part removed, if necessary, using the rounding mode in the decimal context.
No flags, not even Inexact
, are set as long as the
argument is a decnum
(unless the argument is a signaling NaN).
The result may have a positive exponent.
Uses the C library function decNumberToIntegralValue()
.
decnum:trim
decnum:trim () decNumber.trim (decarg)
Returns a decimal number that is the argument with any insignificant trailing zeros removed. That is, if the number has any fractional trailing zeros they are removed by dividing the coefficient by the appropriate power of ten and adjusting the exponent accordingly.
Uses the C library function decNumberTrim()
.
decnum:xor
decnum:xor (decarg) decNumber.xor (decarg, decarg)
Returns a decimal number that is the digitwise logical exclusive or of the arguments. Note that all digits of the arguments must be 0 or 1 or else this operation returns NaN,
Uses the C library function decNumberXor()
.
Comparisons and Predicates
decnum:class
decnum:class () decNumber.class (decarg)
Returns the class of a decNumber. No error is possible. The class is one of the decNumber Classifications.
Uses the C library function decNumberClass()
.
decnum:classasstring
decnum:classasstring () decNumber.classasstring (decarg)
Returns the class of a decNumber as a string. No error is possible. The class is one of "Infinity", "Normal", "Subnormal", "Zero", "+Zero", "+Subnormal", "+Normal", "+Infinity", "NaN", "sNaN", or "Invalid"
Uses the C library functions decNumberClass()
and
decNumberClassToString()
.
classtostring
decNumber.classtostring (enum)
Converts the Classifications of a decNumber to a string. No error is possible. The class is one of "Infinity", "Normal", "Subnormal", "Zero", "+Zero", "+Subnormal", "+Normal", "+Infinity", "NaN", "sNaN", or "Invalid".
Uses the C library function decNumberClassToString()
.
decnum:compare
decnum:compare (decarg) decNumber.compare (decarg, decarg)
Returns a decimal number that is the comparison of its arguments numerically. If the left (1st) argument is less than the right (2nd) argument then the result is 1. If they are equal (that is, when subtracted the result would be 0), then the result is 0. If the left (1st) argument is greater than the right (2nd) argument then the result is 1. If the operands are not comparable (that is, one or both is a NaN) then the result is NaN.
Uses the C library function decNumberCompare()
.
decnum:comparetotal
decnum:comparetotal (decarg) decNumber.comparetotal (decarg, decarg)
Returns a decimal number that is the comparison of its arguments
numerically using the IEEE 754r proposed ordering. The result is the
similar to decnum:compare
above, except that NaN
is never returned. The total order differs from the numerical
comparison in that:
NaN < sNaN < Infinity < finites < 0 < +0 < +finites < +Infinity < +sNaN < +NaN.
Also, 1.000 < 1.0
(etc.) and NaNs are ordered by payload.
Uses the C library function decNumberCompareTotal()
.
decnum:comparetotalmag
decnum:comparetotalmag (decarg) decNumber.comparetotalmag (decarg, decarg)
Returns a decimal number that is the comparison of the magnitude of
its arguments using the IEEE 754r proposed ordering. It is identical
to decnum:comparetotal
above except that
the signs of the operands are ignored and taken to be 0 (nonnegative).
Uses the C library function decNumberCompareTotalMag()
.
decnum:eq
decnum:eq (decarg) decnum:__eq (decarg) decNumber.eq (<decarg>, <decarg>)
Returns a boolean that is true when the arguments are equal, false otherwise.
Note that by binding the method __eq
to this function, the Lua
equality operators (==
and ~=
) may be used with a decnum
on the left and a decnum
on the right.
Uses the C library functions decNumberCompare()
and
decNumberIsZero()
.
decnum:iscanonical
decnum:iscanonical () decNumber.iscanonical (decarg)
Returns true always, because decNumbers always have canonical
encodings (the function is provided for compatibility with the
IEEE 754r operation isCanonical
). No error is possible.
Uses the C library function decNumberIsCanonical()
.
decnum:isfinite
decnum:isfinite () decNumber.isfinite (decarg)
Returns a boolean that is true if the argument is finite, false otherwise (that is, the argument is an infinity or a NaN). No error is possible.
Uses the C library function decNumberIsFinite()
.
decnum:isinfinite
decnum:isinfinite () decNumber.isinfinite (decarg)
Returns a boolean that is true if the argument is infinite, false otherwise. No error is possible.
Uses the C library function decNumberIsInfinite()
.
decnum:isnan
decnum:isnan () decNumber.isnan (decarg)
Returns a boolean that is true if the argument is a NaN (quiet or signaling), false otherwise. No error is possible.
Uses the C library function decNumberIsNaN()
.
decnum:isnegative
decnum:isnegative () decNumber.isnegative (decarg)
Returns a boolean that is true if the argument is is normal (that is, finite, nonzero, and not subnormal), false otherwise. No error is possible.
Uses the C library function C<decNumberIsNegative()>.
decnum:isnormal
decnum:isnormal () decNumber.isnormal (decarg)
Returns a boolean that is true if the argument is negative, false otherwise. No error is possible.
Uses the C library function decNumberIsNormal()
.
decnum:isqnan
decnum:isqnan () decNumber.isqnan (decarg)
Returns a boolean that is true if the argument is a quiet NaN, false otherwise. No error is possible.
Uses the C library function decNumberIsQNaN()
.
decnum:issnan
decnum:issnan () decNumber.issnan (decarg)
Returns a boolean that is true if the argument is a signaling NaN, false otherwise. No error is possible.
Uses the C library function decNumberIsSNaN()
.
decnum:isspecial
decnum:isspecial () decNumber.isspecial (decarg)
Returns a boolean that is true if the argument has a special
value (Infinity or NaN), false otherwise; it is the inversion of
decnum:isfinite
. No error is possible.
Uses the C library function decNumberIsSpecial()
.
decnum:issubnormal
decnum:issubnormal () decNumber.issubnormal (decarg)
Returns a boolean that is true if the argument is subnormal (that is, finite, nonzero, and not in the range of normal values), false otherwise. No error is possible.
Uses the C library function decNumberIsSubnormal()
.
decnum:iszero
decnum:iszero decNumber.iszero (decarg)
Returns a boolean that is true if the argument is zero, false otherwise. No error is possible.
Uses the C library function decNumberIsZero()
.
decnum:le
decnum:le (decarg) decnum:__le (decarg) decNumber.le (<decarg>, <decarg>)
Returns a boolean that is true when left (1st) argument is less than or equal to the right (2nd) argument, false otherwise.
Note that by binding the method __le
to this function, the Lua
comparison operators (<=
and >=
) may be used with a
decnum
on the left and a decnum
on the right.
Uses the C library functions decNumberCompare()
decNumberIsNegative()
and decNumberIsZero()
.
decnum:lt
decnum:lt (decarg) decnum:__lt (decarg) decNumber.lt (<decarg>, <decarg>)
Returns a boolean that is true when left (1st) argument is less than the right (2nd) argument, false otherwise.
Note that by binding the method __lt
to this function, the Lua
comparison operators (<
and >
) may be used with a
decnum
on the left and a decnum
on the right. Lua also assumes
that a <= b
is equivalent to not (b < a)
which in the
presence of NaNs may or may not be what you want  if not, use
decnum:compare
directly.
Uses the C library functions decNumberCompare()
and
decNumberIsNegative()
.
decnum:radix
decnum:radix () decNumber.radix (decarg)
Returns the radix (number base) used by the decNumber package. This always returns 10. No error is possible..
Uses the C library function decNumberRadix()
.
Operations on Random States
The following functions operate on random states.
The random number generator in the ldecNumber package is based on a lagged Fibonacci generator ("LFIB4"). George Marsaglia has this to say about LFIB4:
LFIB4 is an extension of what I have previously defined as a lagged Fibonacci generator ... I have developed the 4lag generator LFIB4 using addition ... Its period is 2^31*(2^2561), about 2^287, and it seems to pass all tests  in particular, those of the kind for which 2lag generators using +,, xor seem to fail.
The ldecNumber package uses LFIB4 to produce a stream of bits in
10bit chunks. This is convenient for making decimal numbers in
multiples of three decimal digits, and fits with the default setting
of the decNumber compile time parameter DECDPUN
. If you change
DECDPUN
then you may not be able to use the ldecNumber package's
random states without modification to the C code. There is a compile
time setting LDN_ENABLE_RANDOM
that should be defined to 0 to
disable random state features.
The ldecNumber package random state code has been tested with L'Ecuyer and Simard's TestU01 Crush  see http://www.iro.umontreal.ca/~simardr/testu01/tu01.html
========= Summary results of Crush ========= Version: TestU011.1 Generator: Generator dec12 Number of statistics: 144 Total CPU time: 02:55:11.06 All tests were passed
While this confers a great deal of confidence in the quality of the generator, two caveats are in order:

Crush uses IEEE doubles, and so the quality of the generator with more than a dozen or so digits is untested, though believed to be good

This generator was not designed for cryptographic use, and so is probably only useful for its intended applications: simulation and testing
decNumber.randomstate
decNumber.randomstate (a [, b [, c [, d]]])
Creates and returns a new random state decrst
. If any arguments
are not supplied, defaults are provided. The arguments a
, b
,
c
, and d
are used as inputs to the random number generator
KISS to initialize the random state.
The random state userdata has one method: __call
. This means that
the random state may be used as a function to return random values.
decrst:__call
decrst(digits [, exponent])
Returns a new random decimal number. If supplied, digits
is the
number of decimal digits in the new random decimal number; the default
is 12. If supplied, exponent
is the exponent of the new random
decimal number; the default is digits
so the new random decimal
number is between zero (inclusive) and one (exclusive).
VERSION
This is ldecNumber version 21.
CREDITS
ldecNumber was developed by Doug Currie, Londonderry, NH, USA.
decNumber was developed by Mike Cowlishaw at IBM.
LICENSE
The ldecNumber distribution includes the C source code of the wrapper itself as a Lua module, a Makefile, examples, test code, and the decNumber source code from IBM. The decNumber code is licensed as follows (see ICUlicense.html in the distribution):
ICU License  ICU 1.8.1 and later
COPYRIGHT AND PERMISSION NOTICE
Copyright (c) 19952005 International Business Machines Corporation and others All rights reserved.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, provided that the above copyright notice(s) and this permission notice appear in all copies of the Software and that both the above copyright notice(s) and this permission notice appear in supporting documentation.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
Except as contained in this notice, the name of a copyright holder shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization of the copyright holder.

All trademarks and registered trademarks mentioned herein are the property of their respective owners.
ldecNumber License
The nonIBM Lua decNumber code and documentation are:
* Copyright (c) 20067 Doug Currie, Londonderry, NH
and licensed under the same terms as the ICU License, above.