Damm algorithm: Difference between revisions
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(Draft Damm algorithm task) |
m (Make it static const, this prevents compiler from building the table on stack, which is somewhat silly.) |
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bool damm(unsigned char *input, size_t length) { |
bool damm(unsigned char *input, size_t length) { |
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unsigned char table[10][10] = { |
static const unsigned char table[10][10] = { |
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{0, 3, 1, 7, 5, 9, 8, 6, 4, 2}, |
{0, 3, 1, 7, 5, 9, 8, 6, 4, 2}, |
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{7, 0, 9, 2, 1, 5, 4, 8, 6, 3}, |
{7, 0, 9, 2, 1, 5, 4, 8, 6, 3}, |
Revision as of 17:25, 29 May 2017
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>
- include <stddef.h>
- include <stdio.h>
bool damm(unsigned char *input, size_t length) {
static const 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>