perl/lib/integer.pm

package integer;

our $VERSION = '1.00';

=head1 NAME

integer - Perl pragma to use integer arithmetic instead of floating point

=head1 SYNOPSIS

    use integer;
    $x = 10/3;
    # $x is now 3, not 3.33333333333333333

=head1 DESCRIPTION

This tells the compiler to use integer operations from here to the end
of the enclosing BLOCK.  On many machines, this doesn't matter a great
deal for most computations, but on those without floating point
hardware, it can make a big difference in performance.

Note that this only affects how most of the arithmetic and relational
B<operators> handle their operands and results, and B<not> how all
numbers everywhere are treated.  Specifically, C<use integer;> has the
effect that before computing the results of the arithmetic operators
(+, -, *, /, %, +=, -=, *=, /=, %=, and unary minus), the comparison
operators (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (|, &,
^, <<, >>, |=, &=, ^=, <<=, >>=), the operands have their fractional
portions truncated (or floored), and the result will have its
fractional portion truncated as well.  In addition, the range of
operands and results is restricted to that of familiar two's complement
integers, i.e., -(2**31) .. (2**31-1) on 32-bit architectures, and
-(2**63) .. (2**63-1) on 64-bit architectures.  For example, this code

    use integer;
    $x = 5.8;
    $y = 2.5;
    $z = 2.7;
    $a = 2**31 - 1;  # Largest positive integer on 32-bit machines
    $, = ", ";
    print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1;

will print:  5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648

Note that $x is still printed as having its true non-integer value of
5.8 since it wasn't operated on.  And note too the wrap-around from the
largest positive integer to the largest negative one.   Also, arguments
passed to functions and the values returned by them are B<not> affected
by C<use integer;>.  E.g.,

    srand(1.5);
    $, = ", ";
    print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);

will give the same result with or without C<use integer;>  The power
operator C<**> is also not affected, so that 2 ** .5 is always the
square root of 2.  Now, it so happens that the pre- and post- increment
and decrement operators, ++ and --, are not affected by C<use integer;>
either.  Some may rightly consider this to be a bug -- but at least it's
a long-standing one.

Finally, C<use integer;> also has an additional affect on the bitwise
operators.  Normally, the operands and results are treated as
B<unsigned> integers, but with C<use integer;> the operands and results
are B<signed>.  This means, among other things, that ~0 is -1, and -2 &
-5 is -6.

Internally, native integer arithmetic (as provided by your C compiler)
is used.  This means that Perl's own semantics for arithmetic
operations may not be preserved.  One common source of trouble is the
modulus of negative numbers, which Perl does one way, but your hardware
may do another.

    % perl -le 'print (4 % -3)'
    -2
    % perl -Minteger -le 'print (4 % -3)'
    1

See L<perlmodlib/"Pragmatic Modules">, L<perlop/"Integer Arithmetic">

=cut

$integer::hint_bits = 0x1;

sub import {
    $^H |= $integer::hint_bits;
}

sub unimport {
    $^H &= ~$integer::hint_bits;
}

1;
Revision:	1.1
Committed:	Thu Jun 30 14:27:09 2005 UTC (21 years, 3 months ago) by root
Branch:	MAIN
CVS Tags:	PERL-5-8-7, HEAD
Branch point for:	PERL
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	package integer;
2
3			our $VERSION = '1.00';
4
5			=head1 NAME
6
7			integer - Perl pragma to use integer arithmetic instead of floating point
8
9			=head1 SYNOPSIS
10
11			use integer;
12			$x = 10/3;
13			# $x is now 3, not 3.33333333333333333
14
15			=head1 DESCRIPTION
16
17			This tells the compiler to use integer operations from here to the end
18			of the enclosing BLOCK. On many machines, this doesn't matter a great
19			deal for most computations, but on those without floating point
20			hardware, it can make a big difference in performance.
21
22			Note that this only affects how most of the arithmetic and relational
23			B<operators> handle their operands and results, and B<not> how all
24			numbers everywhere are treated. Specifically, C<use integer;> has the
25			effect that before computing the results of the arithmetic operators
26			(+, -, , /, %, +=, -=, =, /=, %=, and unary minus), the comparison
27			operators (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (\|, &,
28			^, <<, >>, \|=, &=, ^=, <<=, >>=), the operands have their fractional
29			portions truncated (or floored), and the result will have its
30			fractional portion truncated as well. In addition, the range of
31			operands and results is restricted to that of familiar two's complement
32			integers, i.e., -(231) .. (231-1) on 32-bit architectures, and
33			-(263) .. (263-1) on 64-bit architectures. For example, this code
34
35			use integer;
36			$x = 5.8;
37			$y = 2.5;
38			$z = 2.7;
39			$a = 2**31 - 1; # Largest positive integer on 32-bit machines
40			$, = ", ";
41			print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1;
42
43			will print: 5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648
44
45			Note that $x is still printed as having its true non-integer value of
46			5.8 since it wasn't operated on. And note too the wrap-around from the
47			largest positive integer to the largest negative one. Also, arguments
48			passed to functions and the values returned by them are B<not> affected
49			by C<use integer;>. E.g.,
50
51			srand(1.5);
52			$, = ", ";
53			print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);
54
55			will give the same result with or without C<use integer;> The power
56			operator C<> is also not affected, so that 2 .5 is always the
57			square root of 2. Now, it so happens that the pre- and post- increment
58			and decrement operators, ++ and --, are not affected by C<use integer;>
59			either. Some may rightly consider this to be a bug -- but at least it's
60			a long-standing one.
61
62			Finally, C<use integer;> also has an additional affect on the bitwise
63			operators. Normally, the operands and results are treated as
64			B<unsigned> integers, but with C<use integer;> the operands and results
65			are B<signed>. This means, among other things, that ~0 is -1, and -2 &
66			-5 is -6.
67
68			Internally, native integer arithmetic (as provided by your C compiler)
69			is used. This means that Perl's own semantics for arithmetic
70			operations may not be preserved. One common source of trouble is the
71			modulus of negative numbers, which Perl does one way, but your hardware
72			may do another.
73
74			% perl -le 'print (4 % -3)'
75			-2
76			% perl -Minteger -le 'print (4 % -3)'
77			1
78
79			See L<perlmodlib/"Pragmatic Modules">, L<perlop/"Integer Arithmetic">
80
81			=cut
82
83			$integer::hint_bits = 0x1;
84
85			sub import {
86			$^H \|= $integer::hint_bits;
87			}
88
89			sub unimport {
90			$^H &= ~$integer::hint_bits;
91			}
92
93			1;