Re^2: Print Number With Implied Decimal Point

[Eliya]

use bigint applied globally severely distorts the results.

As both of your test cases work on strings anyway, you'd get a more useful comparison when restricting the scope of bigint to where it's required.

With your original version, I get on my machine:

        Rate substr  regex
substr 481/s     --   -14%
regex  558/s    16%     --

while with the restricted scope of bigint, I get

#!/usr/bin/perl
use warnings;
use strict;
use feature 'say';
use Benchmark qw/cmpthese/;

my @list;
{
    use bigint;
    
    my @chars = ('0' .. '9', 'a' .. 'f');
    
    @list = map {join q(), map $chars[rand @chars], 1 .. 32} 1 .. 100;
    say for @list;
    $_ = (hex $_)."" for @list;
    say for @list;
}

cmpthese(0, {
              substr => sub {
                  my @l = @list;
                  substr $_, -2, 0, '.' for @l;
              },
              regex => sub {
                  my @l = @list;
                  s/(..)$/.$1/ for @l;
              }
});

__END__
          Rate  regex substr
regex   5672/s     --   -80%
substr 28469/s   402%     --

[kennethk]

Note that with a properly crafted regex, the timing difference between it and substr is pretty small; limiting the scope of bigint and using the look-ahead regex from Re^2: Print Number With Implied Decimal Point:

          Rate  regex substr regex2
regex   2926/s     --   -78%   -80%
substr 13087/s   347%     --   -11%
regex2 14782/s   405%    13%     --

Update: see Re^2: Print Number With Implied Decimal Point

[Eliya]

the timing difference between it and substr is pretty small

Yes, sure.  My main point was the side effects of applying use bigint globally (which completely washes out any difference there might be), and not so much to support that substr is faster than regex.

[j355ga]

Limiting the bigint scope makes a HUGE difference in my tests. 2,100 rows per second vs 700 per sec. Thanks for the tip!