lib/perl5/5.6.1/integer.pm

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