Converted a hardcoded version of yours to Inline::C, and it's pretty much the same performance as BrowserUK's Inline::C: 
$ perl ./script
Benchmark: timing 500 iterations of Inline::C (AnomalousMonk), Inline::C (BrowserUK)...
Inline::C (AnomalousMonk):  6 wallclock secs ( 6.21 usr +  0.00 sys =  6.21 CPU) @ 80.52/s (n=500)
Inline::C (BrowserUK):  6 wallclock secs ( 6.14 usr +  0.00 sys =  6.14 CPU) @ 81.43/s (n=500)
Appreciate it! Conversion below: 
int cd4( char *ccn ) {
    int total = 0;
    int i;
    int co9[]={0,2,4,6,8,1,3,5,7,9};
    int straight[]={1,3,5,7,9,11,13};
    int adjusted[]={0,2,4,6,8,10,12,14};
    for (i=0;i<7;i++) {
        total += ccn[straight[i]]-48;
    }
    for (i=0;i<8;i++) {
        total += co9[ccn[adjusted[i]]-48];
    }
    total *=9;
    return total %10;
}

[download]

In reply to Re^2: Faster Luhn Check Digit Calculation? by kschwab
in thread Faster Luhn Check Digit Calculation? by kschwab

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.