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author | Karl Berry <karl@freefriends.org> | 2005-12-28 00:07:27 +0000 |
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committer | Karl Berry <karl@freefriends.org> | 2005-12-28 00:07:27 +0000 |
commit | 30dd9f517c9c093ff3319061647a4555264f7914 (patch) | |
tree | 0d7a349bf99be5a42cc9c5a80a30f3b7136c4ccd /Master/xemtex/perl/lib/integer.pm | |
parent | 08ab8dce83f53b0f915cb66a37bbc8478b22c307 (diff) |
trunk
git-svn-id: svn://tug.org/texlive/trunk@9 c570f23f-e606-0410-a88d-b1316a301751
Diffstat (limited to 'Master/xemtex/perl/lib/integer.pm')
-rw-r--r-- | Master/xemtex/perl/lib/integer.pm | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/Master/xemtex/perl/lib/integer.pm b/Master/xemtex/perl/lib/integer.pm new file mode 100644 index 00000000000..caa1ea6951f --- /dev/null +++ b/Master/xemtex/perl/lib/integer.pm @@ -0,0 +1,93 @@ +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; |