Well, about the onlything I can add is that I looked into Knuth's AoP and found algoithm P (1.3.2) which is for calculating the first N primes. I found it interesting as it was bit hard to convert the pseudocode* he had to perl. I switched around your code to do the same, and here they are: 

sub make_primes_ambrus {
    my $count=shift;
    my @primes=(2);
    my( $n, $p, $sqrp);
    NLOOP:
    for ($n=3; @primes<$count; $n+=2) {
        $sqrp = sqrt($n) + 0.5;
        for $p (@primes) {
                $sqrp < $p and last;
                0 == $n % $p and next NLOOP;
        }
        push @primes, $n
    }
    return \@primes;
}

sub make_primes_knuth  {
    my $count=shift;
    my @primes=(2);
    my $n=3;
    PRIME:
    while (@primes<$count) {
        push @primes,$n;
        while ( $n+=2 ) {
            for my $p (@primes) {
                my $r=$n % $p;
                last if !$r;
                # According to Knuth the proof of the vaildity 
                # of the following test "is interesting and a little 
                # unusual".
                next PRIME if int($n/$p) <= $p;
            }
        }
    }
    return \@primes;
}

[download]

Incidentally, part of the issue for my original problem is that im generating a random prime relatively rarely, and as a fresh process every time. So the time (and hassle coding) to produce a table of primes to use for the div technique is not really necessary. Doing a brute force check on each random number in turn is just fine for me here.

* (Incidentally is there any easy way to get $Q and $R from $x/$y where Q is the quotient and R is the remainder? I used $Q=int($x/$y); and $R=$X % $Y; but i wonder if there is a better way, obviously repeated subtraction would leave an integer remainer somewhere, but given todays chip design is that actually more efficient than doing div and mod as seperate tasks? )

---
$world=~s/war/peace/g

In reply to Re: Simple primality testing by demerphq
in thread Simple primality testing by ambrus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.