note
Athanasius
<p>Although <tt>glob</tt> performs well for small word sizes, for larger sizes a hand-rolled loop is much faster:</p>
<code>
#! perl
use strict;
use warnings;
use Benchmark qw(cmpthese);
cmpthese(1, {
'loop' => sub { my @p = permute_loop(10); print 'loop: ', scalar @p, "\n"; },
'glob' => sub { my @q = permute_glob(10); print 'glob: ', scalar @q, "\n"; },
});
sub permute_glob
{
my ($size) = @_;
my $r = 'A,T,G,C';
return glob "{$r}" x $size;
}
sub permute_loop
{
my ($size) = @_;
my @a = qw(A T G C);
while (--$size)
{
@a = map { $_ . 'A', $_ . 'T', $_ . 'G', $_ . 'C' } @a;
}
return @a;
}
</code>
<p>Output:</p>
<code>
glob: 1048576
(warning: too few iterations for a reliable count)
loop: 1048576
(warning: too few iterations for a reliable count)
s/iter glob loop
glob 281 -- -98%
loop 4.60 6011% --
</code>
<p>Hope that helps,</p>
<!-- Node text goes above. Div tags should contain sig only -->
<div class="pmsig"><div class="pmsig-968231">
<p>Athanasius <font color=#008000><°(((><</font> <i>contra mundum</i></p>
</div></div>
991276
991276