Function levenshtein

levenshtein.c:41–86

* This function implements the Damerau-Levenshtein algorithm to * calculate a distance between strings. * * Basically, it says how many letters need to be swapped, substituted, * deleted from, or added to string1, at least, to get string2. * * The idea is to build a distance matrix for the substrings of both * strings. To avoid a large space complexity, only the last three rows * are kept

 * Note that this algorithm calculates a distance _iff_ d == a.
 */
int levenshtein(const char *string1, const char *string2,
		int w, int s, int a, int d)
{
	int len1 = strlen(string1), len2 = strlen(string2);
	int *row0, *row1, *row2;
	int i, j;

	ALLOC_ARRAY(row0, len2 + 1);
	ALLOC_ARRAY(row1, len2 + 1);
	ALLOC_ARRAY(row2, len2 + 1);

	for (j = 0; j <= len2; j++)
		row1[j] = j * a;
	for (i = 0; i < len1; i++) {
		int *dummy;

		row2[0] = (i + 1) * d;
		for (j = 0; j < len2; j++) {
			/* substitution */
			row2[j + 1] = row1[j] + s * (string1[i] != string2[j]);
			/* swap */
			if (i > 0 && j > 0 && string1[i - 1] == string2[j] &&
					string1[i] == string2[j - 1] &&
					row2[j + 1] > row0[j - 1] + w)
				row2[j + 1] = row0[j - 1] + w;
			/* deletion */
			if (row2[j + 1] > row1[j + 1] + d)
				row2[j + 1] = row1[j + 1] + d;
			/* insertion */
			if (row2[j + 1] > row2[j] + a)
				row2[j + 1] = row2[j] + a;
		}

		dummy = row0;
		row0 = row1;
		row1 = row2;
		row2 = dummy;
	}

	i = row1[len2];
	free(row0);
	free(row1);
	free(row2);

	return i;
}