Are you sure the regex engine isn't "cheating" by caching something? 
#!/usr/bin/perl
use strict;
use warnings;
use Time::HiRes qw(time);

my $num = 3_000_000;
my $str = 'x'x$num . 'reg exp' . 'x'x$num; 

my $start = time;

my $res = $str =~ m/reg exp/;

print time - $start, $/;

$start = time;

my $idx = index $str, 'reg exp';

print time - $start, $/;
__END__
0.0114099979400635
0.011760950088501

[download]

Admittedly, index is still a bit slower, but the difference isn't that huge.

BTW on my machine (with perl 5.8.8) the difference isn't there at all: 

         Rate REGEX INDEX
REGEX 87061/s    --   -2%
INDEX 88494/s    2%    --

[download]

The results only differ slightly for 5.10.0. Which perl did you use?

I thought that index and regexes use the same algorithm, but the regex goes through the pain of compiling the regex first

In reply to Re^3: Performance optimization question by moritz
in thread Performance optimization question by vit

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