66 lines
2.2 KiB
C
66 lines
2.2 KiB
C
#include <assert.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <string.h>
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static const int d[][10] = {
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{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
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{2, 3, 4, 0, 1, 7, 8, 9, 5, 6}, {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
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{4, 0, 1, 2, 3, 9, 5, 6, 7, 8}, {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
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{6, 5, 9, 8, 7, 1, 0, 4, 3, 2}, {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
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{8, 7, 6, 5, 9, 3, 2, 1, 0, 4}, {9, 8, 7, 6, 5, 4, 3, 2, 1, 0},
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};
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static const int inv[] = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};
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static const int p[][10] = {
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{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
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{5, 8, 0, 3, 7, 9, 6, 1, 4, 2}, {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
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{9, 4, 5, 3, 1, 2, 6, 8, 7, 0}, {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
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{2, 7, 9, 3, 8, 0, 6, 4, 1, 5}, {7, 0, 4, 6, 9, 1, 3, 2, 5, 8},
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};
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int verhoeff(const char* s, bool validate, bool verbose) {
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if (verbose) {
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const char* t = validate ? "Validation" : "Check digit";
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printf("%s calculations for '%s':\n\n", t, s);
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puts(u8" i n\xE1\xB5\xA2 p[i,n\xE1\xB5\xA2] c");
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puts("------------------");
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}
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int len = strlen(s);
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if (validate)
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--len;
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int c = 0;
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for (int i = len; i >= 0; --i) {
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int ni = (i == len && !validate) ? 0 : s[i] - '0';
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assert(ni >= 0 && ni < 10);
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int pi = p[(len - i) % 8][ni];
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c = d[c][pi];
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if (verbose)
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printf("%2d %d %d %d\n", len - i, ni, pi, c);
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}
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if (verbose && !validate)
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printf("\ninv[%d] = %d\n", c, inv[c]);
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return validate ? c == 0 : inv[c];
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}
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int main() {
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const char* ss[3] = {"236", "12345", "123456789012"};
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for (int i = 0; i < 3; ++i) {
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const char* s = ss[i];
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bool verbose = i < 2;
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int c = verhoeff(s, false, verbose);
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printf("\nThe check digit for '%s' is '%d'.\n", s, c);
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int len = strlen(s);
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char sc[len + 2];
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strncpy(sc, s, len + 2);
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for (int j = 0; j < 2; ++j) {
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sc[len] = (j == 0) ? c + '0' : '9';
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int v = verhoeff(sc, true, verbose);
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printf("\nThe validation for '%s' is %s.\n", sc,
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v ? "correct" : "incorrect");
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}
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}
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return 0;
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}
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