Luhn test of credit card numbers: Difference between revisions

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@@ Line 253: / Line 253: @@
   unsigned int evenSum = 0;
   int i;
+  const int m[] = {0,2,4,6,8,1,3,5,7,9}; // mapping for rule 3
   for (i = strlen(cc) - 1; i >= 0; --i) {
@@ Line 259: / Line 260: @@
       oddSum += digit;
     } else {
-      evenSum += digit / 5 + (2 * digit) % 10;
+      evenSum += m[digit];  // rule 3
     }
     isOdd = !isOdd;