Re: Faster creation of Arrays in XS?

[BrowserUk]

Why not skip the AoAs and return a string with two delimiters? eg. "3:4 6:3 8:3";

It seems to be just as easy, and probably faster to do:

my $diffs = diff( .... );
for my $diff ( split ' ', $diffs ) {
    my( $start, $len ) = split ':', $diff;
    ## use start / len
}

As it is:

my $ref = diff( ... );

for my $pair ( @{ $ref } ) {
    my( $start, $len ) = @{ $pair };
    ## use start / len
}

[wollmers]

This is magnitudes slower:

#!perl
use 5.006;

use strict;
use warnings;

use Benchmark qw(:all) ;
use Data::Dumper;

my $diffs = join(' ', (map { "$_:$_" } (0..49)));

    timethese( 50_000, {
       'split' => sub {
            my $LCS = [];
            for my $diff ( split ' ', $diffs ) {
                my( $x, $y ) = split ':', $diff;
                #push @$LCS, [$x,$y];
            }
        },
    });
############
~/github/LCS-XS/xt$ perl split.t 
Benchmark: timing 50000 iterations of split...
     split:  2 wallclock secs ( 2.04 usr +  0.00 sys =  2.04 CPU) @ 24
+509.80/s (n=50000)

24 kHz without push, with push 11 kHz.

[BrowserUk]

The idea was to build the string in XS and give that to the caller; not build a string and then build the AoAs from the string; which of course will be slower as your still building the AoAs, but also building and the breaking down the string.

Ie. Build the string instead of the AoAs in XS; and give the caller the string instead of the AoAs; thus avoiding the building of the AoAs entirely.

Be sure to preallocate the string to (even much) bigger than will be required and then use set CUR to trim to the final size.