Yes, 2 elements 50 times.

#!perl
use 5.006;

# file: pack.t

use strict;
use warnings;

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

use List::Util qw(pairs);

my @diffs = map { $_,$_; } (0..49);
#print '@diffs: ',Dumper(\@diffs),"\n";

my $packed0 = pack('V*',@diffs);
my $a = [];

#print 'len: ',length( $packed0),"\n";

my $packed = $packed0;
while (length( $packed)) {
    push @$a,[unpack ('VV', substr( $packed, 0, 8, ''))];
}

#print Dumper($a);

    timethese( 50_000, {
       'unpack while' => sub {
            my $packed = $packed0;
            while (length( $packed)) {
                my ($x,$y)= unpack ('VV', substr( $packed, 0, 8, ''));
            }
        },
       'unpack while single' => sub {
            my $packed = $packed0;
            while (length( $packed)) {
                my $x = unpack ('V', substr( $packed, 0, 4, ''));
            }
        },
       'unpack while push' => sub {
            my $packed = $packed0;
            $a = [];
            while (length( $packed)) {
                push @$a,[unpack ('VV', substr( $packed, 0, 8, ''))];
            }
        },
       'unpack for' => sub {
            for ( my $i = 0;$i < length( $packed0)-1; $i += 8 ) {
                my ($x,$y)= unpack ('VV', substr( $packed0, $i, 8));
            } 
        }, 
       'unpack for push' => sub {
            $a = [];
            for ( my $i = 0;$i < length( $packed0)-1; $i += 8 ) {
                push @$a,[unpack ('VV', substr( $packed0, $i, 8))];
            } 
        },        
    });
 ########
$ perl pack.t 
Benchmark: timing 50000 iterations of unpack for, unpack for push, unp
+ack while, unpack while push, unpack while single...
unpack for:  1 wallclock secs ( 1.01 usr +  0.00 sys =  1.01 CPU) @ 49
+504.95/s (n=50000)
unpack for push:  2 wallclock secs ( 1.84 usr +  0.00 sys =  1.84 CPU)
+ @ 27173.91/s (n=50000)
unpack while:  1 wallclock secs ( 0.84 usr +  0.00 sys =  0.84 CPU) @ 
+59523.81/s (n=50000)
unpack while push:  2 wallclock secs ( 1.75 usr +  0.00 sys =  1.75 CP
+U) @ 28571.43/s (n=50000)
unpack while single:  1 wallclock secs ( 1.28 usr +  0.00 sys =  1.28 
+CPU) @ 39062.50/s (n=50000)

[download]

With bitmaps it would be an array of 2 scalars (2 x 64-bit IVs, 53 bits used in the original test case).

In reply to Re^4: Faster creation of Arrays in XS? by wollmers
in thread Faster creation of Arrays in XS? by wollmers

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