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Commit 604ab08

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robertmhaasrobertmhaas
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Add levenshtein_less_equal, optimized version for small distances.
Alexander Korotkov, heavily revised by me.
1 parent 262c1a4 commit 604ab08

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5 files changed

+459
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‎contrib/fuzzystrmatch/fuzzystrmatch.c‎

Lines changed: 31 additions & 213 deletions
Original file line numberDiff line numberDiff line change
@@ -9,15 +9,6 @@
99
* Copyright (c) 2001-2010, PostgreSQL Global Development Group
1010
* ALL RIGHTS RESERVED;
1111
*
12-
* levenshtein()
13-
* -------------
14-
* Written based on a description of the algorithm by Michael Gilleland
15-
* found at http://www.merriampark.com/ld.htm
16-
* Also looked at levenshtein.c in the PHP 4.0.6 distribution for
17-
* inspiration.
18-
* Configurable penalty costs extension is introduced by Volkan
19-
* YAZICI <volkan.yazici@gmail.com>.
20-
*
2112
* metaphone()
2213
* -----------
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* Modified for PostgreSQL by Joe Conway.
@@ -61,6 +52,8 @@ PG_MODULE_MAGIC;
6152
*/
6253
extern Datum levenshtein_with_costs(PG_FUNCTION_ARGS);
6354
extern Datum levenshtein(PG_FUNCTION_ARGS);
55+
extern Datum levenshtein_less_equal_with_costs(PG_FUNCTION_ARGS);
56+
extern Datum levenshtein_less_equal(PG_FUNCTION_ARGS);
6457
extern Datum metaphone(PG_FUNCTION_ARGS);
6558
extern Datum soundex(PG_FUNCTION_ARGS);
6659
extern Datum difference(PG_FUNCTION_ARGS);
@@ -85,16 +78,6 @@ soundex_code(char letter)
8578
return letter;
8679
}
8780

88-
89-
/*
90-
* Levenshtein
91-
*/
92-
#define MAX_LEVENSHTEIN_STRLEN 255
93-
94-
static int levenshtein_internal(text *s, text *t,
95-
int ins_c, int del_c, int sub_c);
96-
97-
9881
/*
9982
* Metaphone
10083
*/
@@ -197,224 +180,59 @@ rest_of_char_same(const char *s1, const char *s2, int len)
197180
return true;
198181
}
199182

200-
/*
201-
* levenshtein_internal - Calculates Levenshtein distance metric
202-
* between supplied strings. Generally
203-
* (1, 1, 1) penalty costs suffices common
204-
* cases, but your mileage may vary.
205-
*/
206-
static int
207-
levenshtein_internal(text *s, text *t,
208-
int ins_c, int del_c, int sub_c)
209-
{
210-
int m,
211-
n,
212-
s_bytes,
213-
t_bytes;
214-
int *prev;
215-
int *curr;
216-
int *s_char_len = NULL;
217-
int i,
218-
j;
219-
const char *s_data;
220-
const char *t_data;
221-
const char *y;
222-
223-
/* Extract a pointer to the actual character data. */
224-
s_data = VARDATA_ANY(s);
225-
t_data = VARDATA_ANY(t);
226-
227-
/* Determine length of each string in bytes and characters. */
228-
s_bytes = VARSIZE_ANY_EXHDR(s);
229-
t_bytes = VARSIZE_ANY_EXHDR(t);
230-
m = pg_mbstrlen_with_len(s_data, s_bytes);
231-
n = pg_mbstrlen_with_len(t_data, t_bytes);
232-
233-
/*
234-
* We can transform an empty s into t with n insertions, or a non-empty t
235-
* into an empty s with m deletions.
236-
*/
237-
if (!m)
238-
return n * ins_c;
239-
if (!n)
240-
return m * del_c;
241-
242-
/*
243-
* For security concerns, restrict excessive CPU+RAM usage. (This
244-
* implementation uses O(m) memory and has O(mn) complexity.)
245-
*/
246-
if (m > MAX_LEVENSHTEIN_STRLEN ||
247-
n > MAX_LEVENSHTEIN_STRLEN)
248-
ereport(ERROR,
249-
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
250-
errmsg("argument exceeds the maximum length of %d bytes",
251-
MAX_LEVENSHTEIN_STRLEN)));
252-
253-
/*
254-
* In order to avoid calling pg_mblen() repeatedly on each character in s,
255-
* we cache all the lengths before starting the main loop -- but if all the
256-
* characters in both strings are single byte, then we skip this and use
257-
* a fast-path in the main loop. If only one string contains multi-byte
258-
* characters, we still build the array, so that the fast-path needn't
259-
* deal with the case where the array hasn't been initialized.
260-
*/
261-
if (m != s_bytes || n != t_bytes)
262-
{
263-
int i;
264-
const char *cp = s_data;
265-
266-
s_char_len = (int *) palloc((m + 1) * sizeof(int));
267-
for (i = 0; i < m; ++i)
268-
{
269-
s_char_len[i] = pg_mblen(cp);
270-
cp += s_char_len[i];
271-
}
272-
s_char_len[i] = 0;
273-
}
274-
275-
/* One more cell for initialization column and row. */
276-
++m;
277-
++n;
278-
279-
/*
280-
* One way to compute Levenshtein distance is to incrementally construct
281-
* an (m+1)x(n+1) matrix where cell (i, j) represents the minimum number
282-
* of operations required to transform the first i characters of s into
283-
* the first j characters of t. The last column of the final row is the
284-
* answer.
285-
*
286-
* We use that algorithm here with some modification. In lieu of holding
287-
* the entire array in memory at once, we'll just use two arrays of size
288-
* m+1 for storing accumulated values. At each step one array represents
289-
* the "previous" row and one is the "current" row of the notional large
290-
* array.
291-
*/
292-
prev = (int *) palloc(2 * m * sizeof(int));
293-
curr = prev + m;
294-
295-
/*
296-
* To transform the first i characters of s into the first 0 characters
297-
* of t, we must perform i deletions.
298-
*/
299-
for (i = 0; i < m; i++)
300-
prev[i] = i * del_c;
301-
302-
/* Loop through rows of the notional array */
303-
for (y = t_data, j = 1; j < n; j++)
304-
{
305-
int *temp;
306-
const char *x = s_data;
307-
int y_char_len = n != t_bytes + 1 ? pg_mblen(y) : 1;
308-
309-
/*
310-
* To transform the first 0 characters of s into the first j
311-
* characters of t, we must perform j insertions.
312-
*/
313-
curr[0] = j * ins_c;
314-
315-
/*
316-
* This inner loop is critical to performance, so we include a
317-
* fast-path to handle the (fairly common) case where no multibyte
318-
* characters are in the mix. The fast-path is entitled to assume
319-
* that if s_char_len is not initialized then BOTH strings contain
320-
* only single-byte characters.
321-
*/
322-
if (s_char_len != NULL)
323-
{
324-
for (i = 1; i < m; i++)
325-
{
326-
int ins;
327-
int del;
328-
int sub;
329-
int x_char_len = s_char_len[i - 1];
330-
331-
/*
332-
* Calculate costs for insertion, deletion, and substitution.
333-
*
334-
* When calculating cost for substitution, we compare the last
335-
* character of each possibly-multibyte character first,
336-
* because that's enough to rule out most mis-matches. If we
337-
* get past that test, then we compare the lengths and the
338-
* remaining bytes.
339-
*/
340-
ins = prev[i] + ins_c;
341-
del = curr[i - 1] + del_c;
342-
if (x[x_char_len-1] == y[y_char_len-1]
343-
&& x_char_len == y_char_len &&
344-
(x_char_len == 1 || rest_of_char_same(x, y, x_char_len)))
345-
sub = prev[i - 1];
346-
else
347-
sub = prev[i - 1] + sub_c;
348-
349-
/* Take the one with minimum cost. */
350-
curr[i] = Min(ins, del);
351-
curr[i] = Min(curr[i], sub);
352-
353-
/* Point to next character. */
354-
x += x_char_len;
355-
}
356-
}
357-
else
358-
{
359-
for (i = 1; i < m; i++)
360-
{
361-
int ins;
362-
int del;
363-
int sub;
183+
#include "levenshtein.c"
184+
#define LEVENSHTEIN_LESS_EQUAL
185+
#include "levenshtein.c"
364186

365-
/* Calculate costs for insertion, deletion, and substitution. */
366-
ins = prev[i] + ins_c;
367-
del = curr[i - 1] + del_c;
368-
sub = prev[i - 1] + ((*x == *y) ? 0 : sub_c);
369-
370-
/* Take the one with minimum cost. */
371-
curr[i] = Min(ins, del);
372-
curr[i] = Min(curr[i], sub);
187+
PG_FUNCTION_INFO_V1(levenshtein_with_costs);
188+
Datum
189+
levenshtein_with_costs(PG_FUNCTION_ARGS)
190+
{
191+
text *src = PG_GETARG_TEXT_PP(0);
192+
text *dst = PG_GETARG_TEXT_PP(1);
193+
int ins_c = PG_GETARG_INT32(2);
194+
int del_c = PG_GETARG_INT32(3);
195+
int sub_c = PG_GETARG_INT32(4);
373196

374-
/* Point to next character. */
375-
x++;
376-
}
377-
}
197+
PG_RETURN_INT32(levenshtein_internal(src, dst, ins_c, del_c, sub_c));
198+
}
378199

379-
/* Swap current row with previous row. */
380-
temp = curr;
381-
curr = prev;
382-
prev = temp;
383200

384-
/* Point to next character. */
385-
y += y_char_len;
386-
}
201+
PG_FUNCTION_INFO_V1(levenshtein);
202+
Datum
203+
levenshtein(PG_FUNCTION_ARGS)
204+
{
205+
text *src = PG_GETARG_TEXT_PP(0);
206+
text *dst = PG_GETARG_TEXT_PP(1);
387207

388-
/*
389-
* Because the final value was swapped from the previous row to the
390-
* current row, that's where we'll find it.
391-
*/
392-
return prev[m - 1];
208+
PG_RETURN_INT32(levenshtein_internal(src, dst, 1, 1, 1));
393209
}
394210

395211

396-
PG_FUNCTION_INFO_V1(levenshtein_with_costs);
212+
PG_FUNCTION_INFO_V1(levenshtein_less_equal_with_costs);
397213
Datum
398-
levenshtein_with_costs(PG_FUNCTION_ARGS)
214+
levenshtein_less_equal_with_costs(PG_FUNCTION_ARGS)
399215
{
400216
text *src = PG_GETARG_TEXT_PP(0);
401217
text *dst = PG_GETARG_TEXT_PP(1);
402218
int ins_c = PG_GETARG_INT32(2);
403219
int del_c = PG_GETARG_INT32(3);
404220
int sub_c = PG_GETARG_INT32(4);
221+
int max_d = PG_GETARG_INT32(5);
405222

406-
PG_RETURN_INT32(levenshtein_internal(src, dst, ins_c, del_c, sub_c));
223+
PG_RETURN_INT32(levenshtein_less_equal_internal(src, dst, ins_c, del_c, sub_c, max_d));
407224
}
408225

409226

410-
PG_FUNCTION_INFO_V1(levenshtein);
227+
PG_FUNCTION_INFO_V1(levenshtein_less_equal);
411228
Datum
412-
levenshtein(PG_FUNCTION_ARGS)
229+
levenshtein_less_equal(PG_FUNCTION_ARGS)
413230
{
414231
text *src = PG_GETARG_TEXT_PP(0);
415232
text *dst = PG_GETARG_TEXT_PP(1);
233+
int max_d = PG_GETARG_INT32(2);
416234

417-
PG_RETURN_INT32(levenshtein_internal(src, dst, 1, 1, 1));
235+
PG_RETURN_INT32(levenshtein_less_equal_internal(src, dst, 1, 1, 1, max_d));
418236
}
419237

420238

‎contrib/fuzzystrmatch/fuzzystrmatch.sql.in‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,14 @@ CREATE OR REPLACE FUNCTION levenshtein (text,text,int,int,int) RETURNS int
1111
AS 'MODULE_PATHNAME','levenshtein_with_costs'
1212
LANGUAGE C IMMUTABLE STRICT;
1313

14+
CREATE OR REPLACE FUNCTION levenshtein_less_equal (text,text,int) RETURNS int
15+
AS 'MODULE_PATHNAME','levenshtein_less_equal'
16+
LANGUAGE C IMMUTABLE STRICT;
17+
18+
CREATE OR REPLACE FUNCTION levenshtein_less_equal (text,text,int,int,int,int) RETURNS int
19+
AS 'MODULE_PATHNAME','levenshtein_less_equal_with_costs'
20+
LANGUAGE C IMMUTABLE STRICT;
21+
1422
CREATE OR REPLACE FUNCTION metaphone (text,int) RETURNS text
1523
AS 'MODULE_PATHNAME','metaphone'
1624
LANGUAGE C IMMUTABLE STRICT;

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