Provided by: libdata-integer-perl_0.004-1_all 
NAME
Data::Integer - details of the native integer data type
SYNOPSIS
use Data::Integer qw(natint_bits);
$n = natint_bits;
# and other constants; see text
use Data::Integer qw(nint sint uint nint_is_sint nint_is_uint);
$ni = nint($ni);
$si = sint($si);
$ui = uint($ui);
if(nint_is_sint($ni)) { ...
if(nint_is_uint($ni)) { ...
use Data::Integer qw(
nint_sgn sint_sgn uint_sgn
nint_abs sint_abs uint_abs
nint_cmp sint_cmp uint_cmp
nint_min sint_min uint_min
nint_max sint_max uint_max
nint_neg sint_neg uint_neg
nint_add sint_add uint_add
nint_sub sint_sub uint_sub
);
$sn = nint_sgn($ni);
$sn = sint_sgn($si);
$sn = uint_sgn($ui);
$ni = nint_abs($ni);
$si = sint_abs($si);
$ui = uint_abs($ui);
@sorted_nints = sort { nint_cmp($a, $b) } @nints;
@sorted_sints = sort { sint_cmp($a, $b) } @sints;
@sorted_uints = sort { uint_cmp($a, $b) } @uints;
$ni = nint_min($na, $nb);
$si = sint_min($sa, $sb);
$ui = uint_min($ua, $ub);
$ni = nint_max($na, $nb);
$si = sint_max($sa, $sb);
$ui = uint_max($ua, $ub);
$ni = nint_neg($ni);
$si = sint_neg($si);
$ui = uint_neg($ui);
$ni = nint_add($na, $nb);
$si = sint_add($sa, $sb);
$ui = uint_add($ua, $ub);
$ni = nint_sub($na, $nb);
$si = sint_sub($sa, $sb);
$ui = uint_sub($ua, $ub);
use Data::Integer qw(
sint_shl uint_shl
sint_shr uint_shr
sint_rol uint_rol
sint_ror uint_ror
);
$si = sint_shl($si, $dist);
$ui = uint_shl($ui, $dist);
$si = sint_shr($si, $dist);
$ui = uint_shr($ui, $dist);
$si = sint_rol($si, $dist);
$ui = uint_rol($ui, $dist);
$si = sint_ror($si, $dist);
$ui = uint_ror($ui, $dist);
use Data::Integer qw(
nint_bits_as_sint nint_bits_as_uint
sint_bits_as_uint uint_bits_as_sint
);
$si = nint_bits_as_sint($ni);
$ui = nint_bits_as_uint($ni);
$ui = sint_bits_as_uint($si);
$si = uint_bits_as_sint($ui);
use Data::Integer qw(
sint_not uint_not
sint_and uint_and
sint_nand uint_nand
sint_andn uint_andn
sint_or uint_or
sint_nor uint_nor
sint_orn uint_orn
sint_xor uint_xor
sint_nxor uint_nxor
sint_mux uint_mux
);
$si = sint_not($si);
$ui = uint_not($ui);
$si = sint_and($sa, $sb);
$ui = uint_and($ua, $ub);
$si = sint_nand($sa, $sb);
$ui = uint_nand($ua, $ub);
$si = sint_andn($sa, $sb);
$ui = uint_andn($ua, $ub);
$si = sint_or($sa, $sb);
$ui = uint_or($ua, $ub);
$si = sint_nor($sa, $sb);
$ui = uint_nor($ua, $ub);
$si = sint_orn($sa, $sb);
$ui = uint_orn($ua, $ub);
$si = sint_xor($sa, $sb);
$ui = uint_xor($ua, $ub);
$si = sint_nxor($sa, $sb);
$ui = uint_nxor($ua, $ub);
$si = sint_mux($sa, $sb, $sc);
$ui = uint_mux($ua, $ub, $uc);
use Data::Integer qw(
sint_madd uint_madd
sint_msub uint_msub
sint_cadd uint_cadd
sint_csub uint_csub
sint_sadd uint_sadd
sint_ssub uint_ssub
);
$si = sint_madd($sa, $sb);
$ui = uint_madd($ua, $ub);
$si = sint_msub($sa, $sb);
$ui = uint_msub($ua, $ub);
($carry, $si) = sint_cadd($sa, $sb, $carry);
($carry, $ui) = uint_cadd($ua, $ub, $carry);
($carry, $si) = sint_csub($sa, $sb, $carry);
($carry, $ui) = uint_csub($ua, $ub, $carry);
$si = sint_sadd($sa, $sb);
$ui = uint_sadd($ua, $ub);
$si = sint_ssub($sa, $sb);
$ui = uint_ssub($ua, $ub);
use Data::Integer qw(natint_hex hex_natint);
print natint_hex($value);
$value = hex_natint($string);
DESCRIPTION
This module is about the native integer numerical data type. A native integer is one of
the types of datum that can appear in the numeric part of a Perl scalar. This module
supplies constants describing the native integer type.
There are actually two native integer representations: signed and unsigned. Both are
handled by this module.
NATIVE INTEGERS
Each native integer format represents a value using binary place value, with some fixed
number of bits. The number of bits is the same for both signed and unsigned
representations. In each case the least-significant bit has the value 1, the next 2, the
next 4, and so on. In the unsigned representation, this pattern continues up to and
including the most-significant bit, which for a 32-bit machine therefore has the value
2^31 (2147483648). The unsigned format cannot represent any negative numbers.
In the signed format, the most-significant bit is exceptional, having the negation of the
value that it does in the unsigned format. Thus on a 32-bit machine this has the value
-2^31 (-2147483648). Values with this bit set are negative, and those with it clear are
non-negative; this bit is also known as the "sign bit".
It is usual in machine arithmetic to use one of these formats at a time, for example to
add two signed numbers yielding a signed result. However, Perl has a trick: a scalar with
a native integer value contains an additional flag bit which indicates whether the signed
or unsigned format is being used. It is therefore possible to mix signed and unsigned
numbers in arithmetic, at some extra expense.
CONSTANTS
Each of the extreme-value constants has two names, a short one and a long one. The short
names are more convenient to use, but the long names are clearer in a context where other
similar constants exist.
Due to the risks of Perl changing the behaviour of a native integer value that has been
involved in floating point arithmetic (see "BUGS"), the extreme-value constants are
actually non-constant functions that always return a fresh copy of the appropriate value.
The returned value is always a pure native integer value, unsullied by floating point or
string operations.
natint_bits
The width, in bits, of the native integer data types.
min_nint
min_natint
The minimum representable value in either representation. This is -2^(natint_bits -
1).
max_nint
max_natint
The maximum representable value in either representation. This is 2^natint_bits - 1.
min_sint
min_signed_natint
The minimum representable value in the signed representation. This is -2^(natint_bits
- 1).
max_sint
max_signed_natint
The maximum representable value in the signed representation. This is 2^(natint_bits
- 1) - 1.
min_uint
min_unsigned_natint
The minimum representable value in the unsigned representation. This is zero.
max_uint
max_unsigned_natint
The maximum representable value in the unsigned representation. This is 2^natint_bits
- 1.
FUNCTIONS
Each "nint_", "sint_", or "uint_" function operates on one of the three integer formats.
"nint_" functions operate on Perl's union of signed and unsigned; "sint_" functions
operate on signed integers; and "uint_" functions operate on unsigned integers. Except
where indicated otherwise, the function returns a value of its primary type.
Parameters A, B, and C, where present, must be numbers of the appropriate type:
specifically, with a numerical value that can be represented in that type. If there are
multiple flavours of zero, due to floating point funkiness, all zeroes are treated the
same. Parameters with other names have other requirements, explained with each function.
The functions attempt to detect unsuitable arguments, and "die" if an invalid argument is
detected, but they can't notice some kinds of incorrect argument. Generally, it is the
caller's responsibility to provide a sane numerical argument, and supplying an invalid
argument will cause mayhem. Only the numeric value of plain scalar arguments is used; the
string value is completely ignored, so dualvars are not a problem.
Canonicalisation and classification
These are basic glue functions.
nint(A)
sint(A)
uint(A)
These functions each take an argument in a specific integer format and return its
numerical value. This is the argument canonicalisation that is performed by all of
the functions in this module, presented in isolation.
nint_is_sint(A)
Takes a native integer of either type. Returns a truth value indicating whether this
value can be exactly represented as a signed native integer.
nint_is_uint(A)
Takes a native integer of either type. Returns a truth value indicating whether this
value can be exactly represented as an unsigned native integer.
Arithmetic
These functions operate on numerical values rather than just bit patterns. They will all
"die" if the true numerical result doesn't fit into the result format, rather than give a
wrong answer.
nint_sgn(A)
sint_sgn(A)
uint_sgn(A)
Returns +1 if the argument is positive, 0 if the argument is zero, or -1 if the
argument is negative.
nint_abs(A)
sint_abs(A)
uint_abs(A)
Absolute value (magnitude, discarding sign).
nint_cmp(A, B)
sint_cmp(A, B)
uint_cmp(A, B)
Arithmetic comparison. Returns -1, 0, or +1, indicating whether A is less than, equal
to, or greater than B.
nint_min(A, B)
sint_min(A, B)
uint_min(A, B)
Arithmetic minimum. Returns the arithmetically lesser of the two arguments.
nint_max(A, B)
sint_max(A, B)
uint_max(A, B)
Arithmetic maximum. Returns the arithmetically greater of the two arguments.
nint_neg(A)
sint_neg(A)
uint_neg(A)
Negation: returns -A.
nint_add(A, B)
sint_add(A, B)
uint_add(A, B)
Addition: returns A + B.
nint_sub(A, B)
sint_sub(A, B)
uint_sub(A, B)
Subtraction: returns A - B.
Bit shifting
These functions all operate on the bit patterns representing integers, mostly ignoring the
numerical values represented. In most cases the results for particular numerical
arguments are influenced by the word size, because that determines where a bit being left-
shifted will drop off the end of the word and where a bit will be shifted in during a
rightward shift.
With the exception of rightward shifts (see below), each pair of functions performs
exactly the same operations on the bit sequences. There inevitably can't be any functions
here that operate on Perl's union of signed and unsigned; you must choose, by which
function you call, which type the result is to be tagged as.
sint_shl(A, DIST)
uint_shl(A, DIST)
Bitwise left shift (towards more-significant bits). DIST is the distance to shift, in
bits, and must be an integer in the range [0, natint_bits). Zeroes are shifted in
from the right.
sint_shr(A, DIST)
uint_shr(A, DIST)
Bitwise right shift (towards less-significant bits). DIST is the distance to shift,
in bits, and must be an integer in the range [0, natint_bits).
When performing an unsigned right shift, zeroes are shifted in from the left. A
signed right shift is different: the sign bit gets duplicated, so right-shifting a
negative number always gives a negative result.
sint_rol(A, DIST)
uint_rol(A, DIST)
Bitwise left rotation (towards more-significant bits, with the most-significant bit
wrapping round to the least-significant bit). DIST is the distance to rotate, in
bits, and must be an integer in the range [0, natint_bits).
sint_ror(A, DIST)
uint_ror(A, DIST)
Bitwise right rotation (towards less-significant bits, with the least-significant bit
wrapping round to the most-significant bit). DIST is the distance to rotate, in bits,
and must be an integer in the range [0, natint_bits).
Format conversion
These functions convert between the various native integer formats by reinterpreting the
bit patterns used to represent the integers. The bit pattern remains unchanged; its
meaning changes, and so the numerical value changes. Perl scalars preserve the numerical
value, rather than just the bit pattern, so from the Perl point of view these are
functions that change numbers into other numbers.
nint_bits_as_sint(A)
Converts a native integer of either type to a signed integer, by reinterpreting the
bits. The most-significant bit (whether a sign bit or not) becomes a sign bit.
nint_bits_as_uint(A)
Converts a native integer of either type to an unsigned integer, by reinterpreting the
bits. The most-significant bit (whether a sign bit or not) becomes an ordinary most-
significant bit.
sint_bits_as_uint(A)
Converts a signed integer to an unsigned integer, by reinterpreting the bits. The
sign bit becomes an ordinary most-significant bit.
uint_bits_as_sint(A)
Converts an unsigned integer to a signed integer, by reinterpreting the bits. The
most-significant bit becomes a sign bit.
Bitwise operations
These functions all operate on the bit patterns representing integers, completely ignoring
the numerical values represented. They are mostly not influenced by the word size, in the
sense that they will produce the same numerical result for the same numerical arguments
regardless of word size. However, a few are affected by the word size: those on unsigned
operands that return a non-zero result if given zero arguments.
Each pair of functions performs exactly the same operations on the bit sequences. There
inevitably can't be any functions here that operate on Perl's union of signed and
unsigned; you must choose, by which function you call, which type the result is to be
tagged as.
sint_not(A)
uint_not(A)
Bitwise complement (NOT).
sint_and(A, B)
uint_and(A, B)
Bitwise conjunction (AND).
sint_nand(A, B)
uint_nand(A, B)
Bitwise inverted conjunction (NAND).
sint_andn(A, B)
uint_andn(A, B)
Bitwise conjunction with inverted argument (A AND (NOT B)).
sint_or(A, B)
uint_or(A, B)
Bitwise disjunction (OR).
sint_nor(A, B)
uint_nor(A, B)
Bitwise inverted disjunction (NOR).
sint_orn(A, B)
uint_orn(A, B)
Bitwise disjunction with inverted argument (A OR (NOT B)).
sint_xor(A, B)
uint_xor(A, B)
Bitwise symmetric difference (XOR).
sint_nxor(A, B)
uint_nxor(A, B)
Bitwise symmetric similarity (NXOR).
sint_mux(A, B, C)
uint_mux(A, B, C)
Bitwise multiplex. The output has a bit from B wherever A has a 1 bit, and a bit from
C wherever A has a 0 bit. That is, the result is (A AND B) OR ((NOT A) AND C).
Machine arithmetic
These functions perform arithmetic operations that are inherently influenced by the word
size. They always produce a well-defined output if given valid inputs. There inevitably
can't be any functions here that operate on Perl's union of signed and unsigned; you must
choose, by which function you call, which type the result is to be tagged as.
sint_madd(A, B)
uint_madd(A, B)
Modular addition. The result for unsigned addition is (A + B) mod 2^natint_bits. The
signed version behaves similarly, but with a different result range.
sint_msub(A, B)
uint_msub(A, B)
Modular subtraction. The result for unsigned subtraction is (A - B) mod
2^natint_bits. The signed version behaves similarly, but with a different result
range.
sint_cadd(A, B, CARRY_IN)
uint_cadd(A, B, CARRY_IN)
Addition with carry. Two word arguments (A and B) and an input carry bit (CARRY_IN,
which must have the value 0 or 1) are all added together. Returns a list of two
items: an output carry and an output word (of the same signedness as the inputs).
Precisely, the output list (CARRY_OUT, R) is such that CARRY_OUT*2^natint_bits + R = A
+ B + CARRY_IN.
sint_csub(A, B, CARRY_IN)
uint_csub(A, B, CARRY_IN)
Subtraction with carry (borrow). The second word argument (B) and an input carry bit
(CARRY_IN, which must have the value 0 or 1) are subtracted from the first word
argument (A). Returns a list of two items: an output carry and an output word (of the
same signedness as the inputs). Precisely, the output list (CARRY_OUT, R) is such
that R - CARRY_OUT*2^natint_bits = A - B - CARRY_IN.
sint_sadd(A, B)
uint_sadd(A, B)
Saturating addition. The result is A + B if that will fit into the result format,
otherwise the minimum or maximum value of the result format is returned depending on
the direction in which the addition overflowed.
sint_ssub(A, B)
uint_ssub(A, B)
Saturating subtraction. The result is A - B if that will fit into the result format,
otherwise the minimum or maximum value of the result format is returned depending on
the direction in which the subtraction overflowed.
String conversion
natint_hex(VALUE)
VALUE must be a native integer value. The function encodes VALUE in hexadecimal,
returning that representation as a string. Specifically, the output is of the form
"s0xdddd", where "s" is the sign and "dddd" is a sequence of hexadecimal digits.
hex_natint(STRING)
Generates and returns a native integer value from a string encoding it in hexadecimal.
Specifically, the input format is "[s][0x]dddd", where "s" is the sign and "dddd" is a
sequence of one or more hexadecimal digits. The input is interpreted case
insensitively. If the value given in the string cannot be exactly represented in the
native integer type, the function "die"s.
The core Perl function "hex" (see "hex" in perlfunc) does a similar job to this
function, but differs in several ways. Principally, "hex" doesn't handle negative
values, and it gives the wrong answer for values that don't fit into the native
integer type. In Perl 5.6 it also gives the wrong answer for values that don't fit
into the native floating point type. It also doesn't enforce strict syntax on the
input string.
BUGS
In Perl 5.6, when a native integer scalar is used in any arithmetic other than
specifically integer arithmetic, it gets partially transformed into a floating point
scalar. Even if its numerical value can be represented exactly in floating point, so that
floating point arithmetic uses the correct numerical value, some operations are affected
by the floatness. In particular, the stringification of the scalar doesn't necessarily
represent its exact value if it is tagged as floating point.
Because of this transforming behaviour, if you need to stringify a native integer it is
best to ensure that it doesn't get used in any non-integer arithmetic first. If an
integer scalar must be used in standard Perl arithmetic, it may be copied first and the
copy operated upon to avoid causing side effects on the original. If an integer scalar
might have already been transformed, it can be cleaned by passing it through the
canonicalisation function "nint". The functions in this module all avoid modifying their
arguments, and always return pristine integers.
Perl 5.8+ still internally modifies integer scalars in the same circumstances, but seems
to have corrected all the misbehaviour that resulted from it.
Also in Perl 5.6, default Perl arithmetic doesn't necessarily work correctly on native
integers. (This is part of the motivation for the myriad arithmetic functions in this
module.) Default arithmetic here is strictly floating point, so if there are native
integers that cannot be exactly represented in floating point then the arithmetic will
approximate the values before operating on them. Perl 5.8+ attempts to use native integer
operations where possible in its default arithmetic, but as of Perl 5.8.8 it doesn't
always succeed. For reliable integer arithmetic, integer operations must still be
requested explicitly.
SEE ALSO
Data::Float, Scalar::Number, perlnumber(1)
AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT
Copyright (C) 2007, 2010 Andrew Main (Zefram) <zefram@fysh.org>
LICENSE
This module is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.