#!/usr/local/bin/perl -w
use strict;

#These variables are user-configurable.
my $countermax = 10000;          #The max number of primes per file. (To regulate file size)
my $primefile = "Primes.seed";    #The location of the seed file. This is needed.
my $path = "./";     #The first part of the path to dump the files in. This must be pre-existing.
my $last = ".txt";                #The extension to append to the filenames. Your choice.
my $beginloc = "00000";           #The number to start counting at when making filenames.

#End users should not edit below this line
my $lowrange = 0;
my $hirange = 0;
my $current = 0;
my $i = 0;
my $primey = 0;
my $counter = 0;
my @parray;
my $outputloc = $beginloc;

#First this looks for a pre-existing primes file
#which has all the primes less than 10000 in it. 
#It needs this file. Assume it is present or
#suggest a better way or something...
open PRIMES, $primefile;
while(<PRIMES>) {
push (@parray, $_);
}
close PRIMES;

open RESULTS, ">".$path.$outputloc.$last;

print "Welcome to the prime number program.\nThis program will tell you every prime number within a certain range.\nPlease enter the lower range now: ";

$lowrange = <STDIN>;
chomp $lowrange;

#Simple idiot-proofing. I didn't bother to check to make
#sure it's actually an integer. What's a good way to 
#do this?
if($lowrange < 0) { $lowrange = 0; print "\nYour number must be positive. I have set it to 0 for you."; }

print "\nHow high should the program search for primes? ";
$hirange = <STDIN>;
chomp $hirange;

if($hirange <= $lowrange) { $hirange = $lowrange + 100;
print "\nYour second number must be at least equal to the first. \nI have arbitratily set it to be 100 greater.\n";
}


print "Now computing the range of all primes between $lowrange and $hirange. \nPlease wait.\n";

#No need to check even numbers, right?
if($lowrange % 2 == 0) { $lowrange++; }

#Of course, since 1 isn't a prime, we have to account
#for that. Mathmaticians, LART me if I'm wrong. 
if($lowrange == 1) { print RESULTS "2\n"; $lowrange = 3; $counter++; }

for($current = $lowrange; $current <= $hirange; $current += 2) {
$primey = 1;

for($i = 0; $parray[$i] <= sqrt($current); $i++) {
if($current % $parray[$i] == 0) { $primey = 0;
$i = 10000;
}
}


if($primey == 1) {
$counter++;
#print "PRIME FOUND: $current\n";
print RESULTS "$current\n";

if($counter%$countermax == 0) {
close RESULTS;
$outputloc++;
print "\nFile full. Currently ".($current *100/$hirange)."\% done.";

open RESULTS, ">".$path.$outputloc.$last;
}
}
}

print "\nTotal amount of primes: $counter \n";
print "Your results have been saved, starting with
".$path.$beginloc.$last."\n\n";