When in doubt add another table: 

my @luhnmap_1 = (0,2,4,6,8,1,3,5,7,9);
my @luhnmap_2 = ();
for my $x (0..9) {
  for my $y (0..9) {
    @luhnmap_2[$y*10+$x]=$luhnmap_1[$y]+$x;
  }
}

sub LUHN10 {
  my $num = shift;
  my $sum = 0;
  while ($str = substr $num, -2, 2, "") {
    $sum+=$bigmap[$str];
  }
  return $sum % 10 ? 0 : 1;
}

[download]

As bonus, if you don't count the additional table code (aw, come on, please :) ), it's shorter! You can increase this speed some more if you want, but the only way to get a huge increase is to create a bigger table (instead of 10 or 100 elements, try 10,000!). Not sure if it's worth going the next step (the memory and upfront cost).

Enjoy,
Gryn

In reply to Re: YAL10CI (Yet Another LUHN-10 Checksum Implementation) by gryng
in thread YAL10CI (Yet Another LUHN-10 Checksum Implementation) by larryl

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.