55 lines
1.1 KiB
C
55 lines
1.1 KiB
C
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/*
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* upc.c - UPC-A validation.
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*
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* A UPC-A barcode is 12 digits. The last digit is a mod-10 checksum over the
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* first 11: digits in odd positions (1,3,5,7,9,11) are weighted x3 and digits
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* in even positions (2,4,6,8,10) x1; the check digit is whatever makes the
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* weighted total a multiple of 10.
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*/
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#include "upc.h"
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static int allDigits(const char *s, int n)
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{
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int i;
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for (i = 0; i < n; i++) {
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if (s[i] < '0' || s[i] > '9')
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return 0;
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}
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return 1;
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}
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int upcCheckDigit(const char *s)
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{
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int i, sum = 0;
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if (!allDigits(s, 11))
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return -1;
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for (i = 0; i < 11; i++) {
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int d = s[i] - '0';
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if ((i % 2) == 0) /* 0-based even index = 1st,3rd,... digit: weight 3 */
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sum += 3 * d;
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else
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sum += d;
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}
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return (10 - (sum % 10)) % 10;
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}
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int upcIsValid(const char *s)
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{
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int n = 0;
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int check;
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while (s[n] != '\0')
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n++;
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if (n != UPC_A_LEN)
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return 0;
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if (!allDigits(s, UPC_A_LEN))
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return 0;
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check = upcCheckDigit(s);
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if (check < 0)
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return 0;
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return (s[11] - '0') == check;
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}
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