I'm trying to squeeze some more speed out of some code that I've got.

The code in question carries out 15 substr operations for each line of input.
I was expecting a single unpack to be faster, however this wasn't the case.

Could anyone explain what's going on?

Which modules could help trace this sort of issue? Things like Devel::DProf aren't quite the right tool.

Cheers.

BazB.

Benchmarks and code follow...

This is perl, v5.8.0 built for i386-linux-thread-multi 
Benchmark: timing 100000 iterations of substr, unpack...

          Rate unpack substr
unpack 40486/s     --   -28%
substr 55866/s    38%     --

[download]
The code containing the pack/substr is generated using positions slurped from a data dictionary, then eval'ed producing the following: 
sub {
  my $line = shift;
  my @data;

  $data[0] = substr($line, 413, 30);
  $data[1] = substr($line, 373, 30);
  $data[2] = substr($line, 343, 30);
# etc... 
  $data[12] = substr($line, 454, 30);
  $data[13] = substr($line, 240, 3);
  $data[14] = substr($line, 236, 4);
  return @data;
};

#-------------------------------------

sub {
  my $line = shift;
  my @data = unpack('@413A30
                     @373A30
                     @343A30
                     # etc...
                     @454A30
                     @240A3
                     @236A4', $line);
};

[download]

In reply to Unexpected: unpack slower than several substr's. Why? by BazB

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