use strict;
use warnings;

use Benchmark qw{ cmpthese };

my $skipper_regex = qr'\d[245680]$';

sub primes_original {
    my $n = shift;
    return if $n < 2;

    my @primes = (2);
    for my $i (3 .. $n) {
        my $sqrt = sqrt $i;
        my $notprime;
        for my $p (@primes) {
            last if $p > $sqrt;

            $notprime = 1, last if 0 == $i % $p;
        }
        push @primes, $i unless $notprime;
    }
    return @primes
}

sub primes_skipper {
    my $n = shift;
    return if $n < 2;

    my @primes = (2);
    for my $i (3 .. $n) {
        next if $i =~ $skipper_regex;
        my $sqrt = sqrt $i;
        my $notprime;
        for my $p (@primes) {
            last if $p > $sqrt;

            $notprime = 1, last if 0 == $i % $p;
        }
        push @primes, $i unless $notprime;
    }
    return @primes
}

##

sub primes_opt_till_11 {
    my $n = shift;
    return if $n < 2;

    my @primes = (2);
    for my $i (3 .. $n) {
				if($i > 2 || $i % 2 == 0){next}
				if($i > 3 || $i % 3 == 0){next}
				if($i > 5 || $i % 5 == 0){next}
				if($i > 7 || $i % 7 == 0){next}
				if($i > 11 || $i % 11 == 0){next}

        my $sqrt = sqrt $i;
        my $notprime;
        for my $p (@primes) {
            last if $p > $sqrt;

            $notprime = 1, last if 0 == $i % $p;
        }
        push @primes, $i unless $notprime;
    }
    return @primes
}
##
use Test::More tests => 1;
is_deeply([primes_original(10000)], [primes_skipper(10000)], "same");

cmpthese(-10,
        {
primes_original => 'primes_original (10000)',
primes_skipper  => 'primes_skipper  (10000)',
primes_opt_till_11  => 'primes_opt_till_11  (10000)',
 });