extra code in pp_concat, Take 2
[p5sagit/p5-mst-13.2.git] / lib / integer.pm
CommitLineData
a0d0e21e 1package integer;
2
8de1277c 3our $VERSION = '1.00';
4
f06db76b 5=head1 NAME
6
34bbe29d 7integer - Perl pragma to use integer arithmetic instead of floating point
f06db76b 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
34bbe29d 17This tells the compiler to use integer operations from here to the end
18of the enclosing BLOCK. On many machines, this doesn't matter a great
19deal for most computations, but on those without floating point
20hardware, it can make a big difference in performance.
f06db76b 21
a4e975fa 22Note that this only affects how most of the arithmetic and relational
23B<operators> handle their operands and results, and B<not> how all
24numbers everywhere are treated. Specifically, C<use integer;> has the
25effect that before computing the results of the arithmetic operators
26(+, -, *, /, %, +=, -=, *=, /=, %=, and unary minus), the comparison
27operators (<, <=, >, >=, ==, !=, <=>), and the bitwise operators (|, &,
28^, <<, >>, |=, &=, ^=, <<=, >>=), the operands have their fractional
29portions truncated (or floored), and the result will have its
30fractional portion truncated as well. In addition, the range of
31operands and results is restricted to that of familiar two's complement
32integers, i.e., -(2**31) .. (2**31-1) on 32-bit architectures, and
33-(2**63) .. (2**63-1) on 64-bit architectures. For example, this code
a3cb178b 34
35 use integer;
34bbe29d 36 $x = 5.8;
37 $y = 2.5;
a4e975fa 38 $z = 2.7;
39 $a = 2**31 - 1; # Largest positive integer on 32-bit machines
34bbe29d 40 $, = ", ";
a4e975fa 41 print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y, $y == $z, $a, $a + 1;
34bbe29d 42
a4e975fa 43will print: 5.8, -5, 7, 3, 2, 10, 1, 2147483647, -2147483648
34bbe29d 44
45Note that $x is still printed as having its true non-integer value of
a4e975fa 465.8 since it wasn't operated on. And note too the wrap-around from the
47largest positive integer to the largest negative one. Also, arguments
48passed to functions and the values returned by them are B<not> affected
49by C<use integer;>. E.g.,
34bbe29d 50
51 srand(1.5);
52 $, = ", ";
53 print sin(.5), cos(.5), atan2(1,2), sqrt(2), rand(10);
54
55will give the same result with or without C<use integer;> The power
56operator C<**> is also not affected, so that 2 ** .5 is always the
a4e975fa 57square root of 2. Now, it so happens that the pre- and post- increment
58and decrement operators, ++ and --, are not affected by C<use integer;>
59either. Some may rightly consider this to be a bug -- but at least it's
60a long-standing one.
34bbe29d 61
a4e975fa 62Finally, C<use integer;> also has an additional affect on the bitwise
63operators. Normally, the operands and results are treated as
64B<unsigned> integers, but with C<use integer;> the operands and results
65are B<signed>. This means, among other things, that ~0 is -1, and -2 &
66-5 is -6.
34bbe29d 67
68Internally, native integer arithmetic (as provided by your C compiler)
69is used. This means that Perl's own semantics for arithmetic
70operations may not be preserved. One common source of trouble is the
71modulus of negative numbers, which Perl does one way, but your hardware
72may do another.
73
74 % perl -le 'print (4 % -3)'
75 -2
76 % perl -Minteger -le 'print (4 % -3)'
77 1
47f6b1df 78
a4e975fa 79See L<perlmodlib/"Pragmatic Modules">, L<perlop/"Integer Arithmetic">
f06db76b 80
81=cut
82
d5448623 83$integer::hint_bits = 0x1;
84
a0d0e21e 85sub import {
d5448623 86 $^H |= $integer::hint_bits;
a0d0e21e 87}
88
89sub unimport {
d5448623 90 $^H &= ~$integer::hint_bits;
a0d0e21e 91}
92
931;