mirror of
https://github.com/git/git.git
synced 2024-10-31 14:27:54 +01:00
b32fa95fd8
Each of these cases can be converted to use ALLOC_ARRAY or
REALLOC_ARRAY, which has two advantages:
1. It automatically checks the array-size multiplication
for overflow.
2. It always uses sizeof(*array) for the element-size,
so that it can never go out of sync with the declared
type of the array.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
86 lines
2.5 KiB
C
86 lines
2.5 KiB
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 substitution, 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)
|
|
{
|
|
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;
|
|
}
|