Hello Monks,

I am trying to figure out why this code performs so poorly against its C counterpart:

Perl (complete program)

#!/usr/bin/perl

OUTER:
for (my $i = 20; ; $i += 20) {
    foreach (my $j = 1; $j < 20; $j++) {
        next OUTER if ($i % $j);
    }
    print "Number: $i\n";
    last;
}

[download]

C (complete program)

#include <stdio.h>

int main(void) {
    int i, j;

    for (i = 20; ; i += 20) {
        for (j = 1; j < 20; j++) {
            if (i % j)
                break;
        }
        if (j == 20) {
            printf("Number: %d\n", i);
            break;
        }
    }

    return 0;
}

[download]

On my machine, the C variant (Linux GCC 4.3.2, no optimization flags, not stripped) runs in 1.36 +/- 0.02 user+system seconds.

The Perl variant (5.10.0) takes 48.7 user+system seconds on the same machine.

Why is Perl so much slower at running the same algorithm? (Actually the C algorithm is slightly worse due to the extra comparison).

Keep in mind, the purpose of the code samples is completely tangential to this discussion--I am seeing similar performance with all tight processing loops. I am aware of the ability to use native C libraries with Perl (and other optimization techniques), but my question is not about optimization. I just want to get a better idea of what is making Perl so terribly slow with simple loops like the above.

In reply to Why is this code so much slower than the same algorithm in C? by wanna_code_perl

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