Verhoeff algorithm: Difference between revisions

=={{header|C}}==

<lang c>#include <assert.h>

#include <stdbool.h>

#include <stdio.h>

#include <string.h>

static const int d[][10] = {

{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},

{2, 3, 4, 0, 1, 7, 8, 9, 5, 6}, {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},

{4, 0, 1, 2, 3, 9, 5, 6, 7, 8}, {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},

{6, 5, 9, 8, 7, 1, 0, 4, 3, 2}, {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},

{8, 7, 6, 5, 9, 3, 2, 1, 0, 4}, {9, 8, 7, 6, 5, 4, 3, 2, 1, 0},

};

static const int inv[] = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};

static const int p[][10] = {

{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},

{5, 8, 0, 3, 7, 9, 6, 1, 4, 2}, {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},

{9, 4, 5, 3, 1, 2, 6, 8, 7, 0}, {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},

{2, 7, 9, 3, 8, 0, 6, 4, 1, 5}, {7, 0, 4, 6, 9, 1, 3, 2, 5, 8},

};

int verhoeff(const char* s, bool validate, bool verbose) {

if (verbose) {

const char* t = validate ? "Validation" : "Check digit";

printf("%s calculations for '%s':\n\n", t, s);

puts(u8" i n\xE1\xB5\xA2 p[i,n\xE1\xB5\xA2] c");

puts("------------------");

}

int len = strlen(s);

if (validate)

--len;

int c = 0;

for (int i = len; i >= 0; --i) {

int ni = (i == len && !validate) ? 0 : s[i] - '0';

assert(ni >= 0 && ni < 10);

int pi = p[(len - i) % 8][ni];

c = d[c][pi];

if (verbose)

printf("%2d %d %d %d\n", len - i, ni, pi, c);

}

if (verbose && !validate)

printf("\ninv[%d] = %d\n", c, inv[c]);

return validate ? c == 0 : inv[c];

}

int main() {

const char* ss[3] = {"236", "12345", "123456789012"};

for (int i = 0; i < 3; ++i) {

const char* s = ss[i];

bool verbose = i < 2;

int c = verhoeff(s, false, verbose);

printf("\nThe check digit for '%s' is '%d'.\n", s, c);

int len = strlen(s);

char sc[len + 2];

strncpy(sc, s, len + 2);

for (int j = 0; j < 2; ++j) {

sc[len] = (j == 0) ? c + '0' : '9';

int v = verhoeff(sc, true, verbose);

printf("\nThe validation for '%s' is %s.\n", sc,

v ? "correct" : "incorrect");

}

}

return 0;

}</lang>

{{out}}

<pre>

Check digit calculations for '236':

i nᵢ p[i,nᵢ] c

------------------

0 0 0 0

1 6 3 3

2 3 3 1

3 2 1 2

inv[2] = 3

The check digit for '236' is '3'.

Validation calculations for '2363':

i nᵢ p[i,nᵢ] c

------------------

0 3 3 3

1 6 3 1

2 3 3 4

3 2 1 0

The validation for '2363' is correct.

Validation calculations for '2369':

i nᵢ p[i,nᵢ] c

------------------

0 9 9 9

1 6 3 6

2 3 3 8

3 2 1 7

The validation for '2369' is incorrect.

Check digit calculations for '12345':

i nᵢ p[i,nᵢ] c

------------------

0 0 0 0

1 5 8 8

2 4 7 1

3 3 6 7

4 2 5 2

5 1 2 4

inv[4] = 1

The check digit for '12345' is '1'.

Validation calculations for '123451':

i nᵢ p[i,nᵢ] c

------------------

0 1 1 1

1 5 8 9

2 4 7 2

3 3 6 8

4 2 5 3

5 1 2 0

The validation for '123451' is correct.

Validation calculations for '123459':

i nᵢ p[i,nᵢ] c

------------------

0 9 9 9

1 5 8 1

2 4 7 8

3 3 6 2

4 2 5 7

5 1 2 5

The validation for '123459' is incorrect.

The check digit for '123456789012' is '0'.

The validation for '1234567890120' is correct.

The validation for '1234567890129' is incorrect.

</pre>