素数を求める(新卒のときの課題)

prime.pl

#!/usr/bin/perl -l
use strict;
use Time::HiRes;

my $start_time = Time::HiRes::time;

main(int($ARGV[0]) || 10_000);

my $end_time = Time::HiRes::time;
my $computation_time = $end_time - $start_time;

print $computation_time;

sub main {
    my $max = shift;
    my $sqrt_max = int sqrt $max;
    my @not_prime;
    my $prime = '2';

    for my $n ( 3 .. $sqrt_max ) {
        (!($n & 0x01) or $not_prime[$n >> 1]) and next;

        $prime .= ",$n";

        for (my ($i, $d) = ($n ** 2, $n * 2); $i <= $max; $i += $d) {
            $not_prime[$i >> 1] = 1;
        }
    }

    for my $n ( $sqrt_max + 1 .. $max ) {
        (!($n & 0x01) or $not_prime[$n >> 1]) or $prime .= ",$n";
    }

    print $prime;
}