# Commits

committed ef4daa7 Merge

Merge branch 'st/levenshtein'

* st/levenshtein:
Document levenshtein.c
Fix deletion of last character in levenshtein distance

# levenshtein.c

` #include "cache.h"`
` #include "levenshtein.h"`
` `
`+/*`
`+ * 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 in memory (if swaps had the same or higher cost as one deletion`
`+ * plus one insertion, only two rows would be needed).`
`+ *`
`+ * At any stage, "i + 1" denotes the length of the current substring of`
`+ * string1 that the distance is calculated for.`
`+ *`
`+ * row2 holds the current row, row1 the previous row (i.e. for the substring`
`+ * of string1 of length "i"), and row0 the row before that.`
`+ *`
`+ * In other words, at the start of the big loop, row2[j + 1] contains the`
`+ * Damerau-Levenshtein distance between the substring of string1 of length`
`+ * "i" and the substring of string2 of length "j + 1".`
`+ *`
`+ * All the big loop does is determine the partial minimum-cost paths.`
`+ *`
`+ * It does so by calculating the costs of the path ending in characters`
`+ * i (in string1) and j (in string2), respectively, given that the last`
`+ * operation is a substition, a swap, a deletion, or an insertion.`
`+ *`
`+ * This implementation allows the costs to be weighted:`
`+ *`
`+ * - w (as in "sWap")`
`+ * - s (as in "Substitution")`
`+ * - a (for insertion, AKA "Add")`
`+ * - d (as in "Deletion")`
`+ *`
`+ * 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)`
` {`
` 					row2[j + 1] > row0[j - 1] + w)`
` 				row2[j + 1] = row0[j - 1] + w;`
` 			/* deletion */`
`-			if (j + 1 < len2 && row2[j + 1] > row1[j + 1] + d)`
`+			if (row2[j + 1] > row1[j + 1] + d)`
` 				row2[j + 1] = row1[j + 1] + d;`
` 			/* insertion */`
` 			if (row2[j + 1] > row2[j] + a)`