If, based on your answers in this thread, ultimate goal is better speed after all (and not mysterious slow-downs on every 10th run, about which I have nothing to add), then as usual in case of large arrays, use PDL;. Second pair of results are for 10x $n.

use warnings;
use strict;

use feature 'say';
use Time::HiRes 'time';

srand( 1 );
my $n = 2e3;
my @input = map int rand 1e5, 1 .. $n;

my ( $check1, $check2 );

{                   # original code
    my $t = time;

    my @max;

    push @max, ( sort { $b <=> $a } @input )[ 0 ];
    my @sums = @input;

    for my $i ( 1 .. $n - 1 ){
    
        my $max = -~0;
        for my $j ( $i .. $n - 1 ){
        # HOT-SPOT {
            ( $sums[ $j - $i ] += $input[ $j ] ) > $max 
                and $max = $sums[ $j - $i ];
        # HOT-SPOT }
        }
        push @max, $max;
    }

    say time - $t;
    $check1 = pack 'I*', @max;
}

{                   # PDL
    my $t = time;

    use PDL;
    use PDL::NiceSlice;
    
    my $sums = zeroes long, scalar @input;
    my $vec  = pdl long, \@input;
    
    my @max = map $sums( 0 : -$_ - 1 )
        -> inplace
        -> plus( $vec( $_ : -1 ), 0 )
        -> maximum
    , 0 .. $#input;

    say time - $t;
    $check2 = pack 'I*', @max;
}

use Test::More;
is $check1, $check2;
done_testing;

__END__

0.148595094680786
0.0387320518493652
ok 1
1..1

14.5055229663849
0.759373903274536
ok 1
1..1

[download]

In reply to Re: Performance issue in the loop. by vr
in thread Performance issue in the loop. by rsFalse

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