Actually, I had previously tried it using assignment rather than push and the difference was so negligable as to be within the bounds of varience from one run to the next. 

C:\test>226666
Benchmark:
running
 substr_it, unpack_it
, each for at least 3 CPU seconds
...

 substr_it:  4 wallclock secs ( 3.17 usr +  0.00 sys =  3.17 CPU) @ 23
+75.99/s (n=7520)

 unpack_it:  4 wallclock secs ( 3.38 usr +  0.00 sys =  3.38 CPU) @ 43
+71.56/s (n=14754)

            Rate substr_it unpack_it
substr_it 2376/s        --      -46%
unpack_it 4372/s       84%        --
Results tally

C:\test>

[download]

I did verify the original as best I could, but as he didn't supply the whole benchmark I had to make a few guesses.

I also attempted to improve both as far as I could as you will see from the update to my first post based upon your suggestion :^)

Older benchmark code for the above results

#! perl -slw
use strict;
use vars qw[$line @s @s2 @u1 @u2];
use Benchmark qw[cmpthese];

$line = (join'','a' .. 'y') x 40;

sub substr_it{
    my @bits;
    $bits[0]  = substr $_[0], 413,  30;
    $bits[1]  = substr $_[0], 373,  30;
    $bits[2]  = substr $_[0], 343,  30;
    $bits[3]  = substr $_[0], 245,  15;
    $bits[4]  = substr $_[0], 679,  30;
    $bits[5]  = substr $_[0],  10,  10;
    $bits[6]  = substr $_[0], 900, 100;
    $bits[7]  = substr $_[0], 500,   2;
    $bits[8]  = substr $_[0], 313,  30;
    $bits[9]  = substr $_[0], 844,  44;
    $bits[10] = substr $_[0], 111,   1;
    $bits[11] = substr $_[0], 100, 100;
    $bits[12] = substr $_[0], 454,  30;
    $bits[13] = substr $_[0], 240,   3;
    $bits[14] = substr $_[0], 236,   4;

    @bits;
}


sub unpack_it{
    my $fmt = '@413A30 @373A30 @343A30 @245A15 @679A30 @10A10 @900A100
+'
            . '@500A2 @313A30 @844A44 @111A1 @100A100 @454A30 @240A3 @
+236A4';

    unpack( $fmt, $_[0]);
}

cmpthese( -3, {
    substr_it    => '@s  = substr_it  $line;',
    unpack_it    => '@u1 = unpack_it  $line;',
});

print 'Results tally';

__END__

[download]

Examine what is said, not who speaks.

The 7th Rule of perl club is -- pearl clubs are easily damaged. Use a diamond club instead.

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

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