dpk’s weblog

This may be old news for people more familiar with perl internals.

dpk@dpk1:~$ perl -version | head -2

This is perl, v5.8.8 built for i486-linux-gnu-thread-multi
dpk@dpk1:~$ cat test1.pl
#!/usr/bin/perl

use strict;

my $x = 0;
while ($x < 100)
{
  &doit();
  $x++;
}

sub doit() {
  my $foo = 'foobar'; my $x = 0; my $y = 0;
  while ($x < 1000000)
  {
    if ($foo eq 'foofoo')
    {
      $y++;
    }
    $x++;
  }
}
dpk@dpk1:~$ perl -d:DProf test1.pl;dprofpp
Total Elapsed Time = 52.07938 Seconds
  User+System Time = 52.07938 Seconds
Exclusive Times
%Time ExclSec CumulS #Calls sec/call Csec/c  Name
 99.9   52.07 52.070    100   0.5207 0.5207  main::doit
 0.00       - -0.000      1        -      -  strict::bits
 0.00       - -0.000      1        -      -  strict::import
 0.00       - -0.000      1        -      -  main::BEGIN

And then:

dpk@dpk1:~$ cat test2.pl
#!/usr/bin/perl

use strict;

my $x = 0;
while ($x < 100)
{
  &doit();
  $x++;
}

sub doit() {
  my $foo = 'foobar'; my $x = 0; my $y = 0;
  while ($x < 1000000)
  {
    if ('foofoo' eq $foo)
    {
      $y++;
    }
    $x++;
  }
}
Total Elapsed Time = 51.31948 Seconds
  User+System Time = 51.30948 Seconds
Exclusive Times
%Time ExclSec CumulS #Calls sec/call Csec/c  Name
 100.   51.31 51.310    100   0.5131 0.5131  main::doit
 0.00       - -0.000      1        -      -  strict::bits
 0.00       - -0.000      1        -      -  strict::import
 0.00       - -0.000      1        -      -  main::BEGIN

I’ve repeated this little test multiple times, with different several different inputs, but the result is always the same. if ('string' eq $variable) is faster than if ($variable eq 'string')