Respected Monks,

This will perhaps go in the history of PerlMonks (and otherwise) as the stupidest prime number detector ever!!, but I am trying to learn how to create modules and needed something to work on. If after checking this script, the Monks here decide that I am too stupid to even attempt to create modules, I can certainly live with it.

So, as shown below, the script detects if the supplied number is a prime or not. If the number is a prime and is 5 or 6 digits, the script becomes somewhat slower. At 7 digit primes, it just starts getting exponentially slower and anything above that, it just hangs.

However, if the number is NOT a prime, and even if it is 20 digits, it shows the output in a flash!!

use strict;
use warnings;
use 5.10.1;
use bignum;
use Time::HiRes qw(gettimeofday tv_interval);

print "Enter the integer: ";
chomp (my $prime_candidate = <STDIN>) ;

exit if $prime_candidate <= 0 && say "$prime_candidate is not a prime.
+";
my $is_prime = 1;

my $start_time = [gettimeofday];
foreach my $each_num (2..$prime_candidate) {
    if ($prime_candidate % $each_num == 0 && $prime_candidate - $each_
+num != 0 ) {
    say "$prime_candidate is not a prime";
    $is_prime = 0;
    exit;
  }
}
my $elapsed_time = tv_interval($start_time);
say "$prime_candidate is a prime " if  $is_prime != 0;
printf "The [$0] script took %2.2f seconds to finish\n", $elapsed_time
+;

[download]

Given below are the outputs: 

$ perl time_is_prime_v1.pl 
Enter the integer: 99929
99929 is a prime 
The [time_is_prime_v1.pl] script took 0.79 seconds to finish

$ perl time_is_prime_v1.pl 
Enter the integer: 999983
999983 is a prime 
The [time_is_prime_v1.pl] script took 7.69 seconds to finish


$ perl time_is_prime_v1.pl 
Enter the integer: 9999991
9999991 is a prime 
The [time_is_prime_v1.pl] script took 73.97 seconds to finish

$ perl time_is_prime_v1.pl 
Enter the integer: 1320486952377516576  
1320486952377516576 is not a prime

[download]

So why have I put up this monstrosity here? I just want to find a way to make it work faster so that I can create a module out of it by doing the required changes, test the output by checking it against the output of Math::Prime::Util and be happy that I've created a module!!. I will not ever dare to put it up on CPAN as I know it's too stupid :D, I just want to play with Perl.

In reply to Stupidest Prime Number detector ever!! by Anonymous Monk

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