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| -rw-r--r-- | lib/integer.pm | 71 |
1 files changed, 47 insertions, 24 deletions
diff --git a/lib/integer.pm b/lib/integer.pm index f019fb3534..f720ce56d0 100644 --- a/lib/integer.pm +++ b/lib/integer.pm @@ -4,7 +4,7 @@ our $VERSION = '1.00'; =head1 NAME -integer - Perl pragma to compute arithmetic in integer instead of double +integer - Perl pragma to use integer arithmetic instead of floating point =head1 SYNOPSIS @@ -14,32 +14,55 @@ integer - Perl pragma to compute arithmetic in integer instead of double =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. +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 affects the operations, not the numbers. If you run this -code +Note that this only affects how certain operators handle their operands +and results, and not all numbers everywhere. Specifically, C<use +integer;> has the effect that before computing the result of X + Y, X - +Y, X / Y, X * Y, X % Y, or -X (unary minus), the operands X and Y have +their fractional portions truncated, and the result will have its +fractional portion truncated as well. For example, this code use integer; - $x = 1.5; - $y = $x + 1; - $z = -1.5; - -you'll be left with C<$x == 1.5>, C<$y == 2> and C<$z == -1>. The $z -case happens because unary C<-> counts as an operation. - -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 + $x = 5.8; + $y = 2.5; + $, = ", "; + print $x, -$x, $x + $y, $x - $y, $x / $y, $x * $y; + +will print: 5.8, -5, 7, 3, 2, 10 + +Note that $x is still printed as having its true non-integer value of +5.8 since it wasn't operated on. Also, arguments passed to functions +and the values returned by them are 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. + +Finally, C<use integer;> also has an affect on the bitwise operators +"&", "|", "^", "~", "<<", and ">>". Normally, the operands and results +are treated as unsigned integers, but with C<use integer;> the operands +and results are 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<perlmod/Pragmatic Modules>. |