Damm algorithm

Damm algorithm is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

The Damm algorithm is a checksum algorithm which detects all single digit errors and adjacent transposition errors. The task is to verify the checksum, stored as last digit of an input.

C

<lang c>#include <stdbool.h>

1. include <stddef.h>
2. include <stdio.h>

bool damm(unsigned char *input, size_t length) {

   unsigned char table[10][10] = {
       {0, 3, 1, 7, 5, 9, 8, 6, 4, 2},
       {7, 0, 9, 2, 1, 5, 4, 8, 6, 3},
       {4, 2, 0, 6, 8, 7, 1, 3, 5, 9},
       {1, 7, 5, 0, 9, 8, 3, 4, 2, 6},
       {6, 1, 2, 3, 0, 4, 5, 9, 7, 8},
       {3, 6, 7, 4, 2, 0, 9, 5, 8, 1},
       {5, 8, 6, 9, 7, 2, 0, 1, 3, 4},
       {8, 9, 4, 5, 3, 6, 2, 0, 1, 7},
       {9, 4, 3, 8, 6, 1, 7, 2, 0, 5},
       {2, 5, 8, 1, 4, 3, 6, 7, 9, 0},
   };
   
   unsigned char interim = 0;
   for (size_t i = 0; i < length; i++) {
       interim = table[interim][input[i]];
   }
   return interim == 0;

}

int main() {

   unsigned char input[4] = {5, 7, 2, 4};
   puts(damm(input, 4) ? "Checksum correct" : "Checksum incorrect");
   return 0;

}</lang>