That's funny, I was converting yours to Inline::C at the same time. 
int cd2(char *number) {
    int i, d, total;
    total=0;
    for (i = 0; i<15; i++) {
        d=number[i]-48;
        if (!(i & 1)) {
            d *=2;
            if (d > 9) {d-=9;}
        }
        total+=d;
    }
    total *=9;
    return total % 10;
}

[download]
And, it is a little faster, appreciate it. 
$perl ./script
Benchmark: timing 200 iterations of Inline::C (BrowserUK-His Conversion), Inline::C (BrowserUK-My Conversion), Inline::C (orig)...
Inline::C (BrowserUK-His Conversion):  2 wallclock secs ( 2.54 usr +  0.00 sys =  2.54 CPU) @ 78.74/s (n=200)
Inline::C (BrowserUK-My Conversion):  3 wallclock secs ( 2.51 usr +  0.00 sys =  2.51 CPU) @ 79.68/s (n=200)
Inline::C (orig):  3 wallclock secs ( 2.97 usr +  0.00 sys =  2.97 CPU) @ 67.34/s (n=200)

In reply to Re^5: Faster Luhn Check Digit Calculation? by kschwab
in thread Faster Luhn Check Digit Calculation? by kschwab

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