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Commit57d9aef

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committed
Teach levenshtein() about multi-byte characters.
Based on a patch by, and further ideas from, Alexander Korotkov.
1 parentad17ff9 commit57d9aef

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2 files changed

+122
-22
lines changed

2 files changed

+122
-22
lines changed

‎contrib/fuzzystrmatch/fuzzystrmatch.c‎

Lines changed: 118 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -5,7 +5,7 @@
55
*
66
* Joe Conway <mail@joeconway.com>
77
*
8-
* $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.c,v 1.33 2010/07/2920:11:48 rhaas Exp $
8+
* $PostgreSQL: pgsql/contrib/fuzzystrmatch/fuzzystrmatch.c,v 1.34 2010/08/02 23:20:23 rhaas Exp $
99
* Copyright (c) 2001-2010, PostgreSQL Global Development Group
1010
* ALL RIGHTS RESERVED;
1111
*
@@ -50,6 +50,7 @@
5050
#include<ctype.h>
5151

5252
#include"fmgr.h"
53+
#include"mb/pg_wchar.h"
5354
#include"utils/builtins.h"
5455

5556
PG_MODULE_MAGIC;
@@ -183,6 +184,18 @@ getcode(char c)
183184
/* These prevent GH from becoming F */
184185
#defineNOGHTOF(c)(getcode(c) & 16)/* BDH */
185186

187+
/* Faster than memcmp(), for this use case. */
188+
staticboolinline
189+
rest_of_char_same(constchar*s1,constchar*s2,intlen)
190+
{
191+
while (len>0)
192+
{
193+
len--;
194+
if (s1[len]!=s2[len])
195+
return false;
196+
}
197+
return true;
198+
}
186199

187200
/*
188201
* levenshtein_internal - Calculates Levenshtein distance metric
@@ -195,16 +208,27 @@ levenshtein_internal(text *s, text *t,
195208
intins_c,intdel_c,intsub_c)
196209
{
197210
intm,
198-
n;
211+
n,
212+
s_bytes,
213+
t_bytes;
199214
int*prev;
200215
int*curr;
216+
int*s_char_len=NULL;
201217
inti,
202218
j;
203-
constchar*x;
219+
constchar*s_data;
220+
constchar*t_data;
204221
constchar*y;
205222

206-
m=VARSIZE_ANY_EXHDR(s);
207-
n=VARSIZE_ANY_EXHDR(t);
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);
208232

209233
/*
210234
* We can transform an empty s into t with n insertions, or a non-empty t
@@ -226,6 +250,28 @@ levenshtein_internal(text *s, text *t,
226250
errmsg("argument exceeds the maximum length of %d bytes",
227251
MAX_LEVENSHTEIN_STRLEN)));
228252

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+
inti;
264+
constchar*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+
229275
/* One more cell for initialization column and row. */
230276
++m;
231277
++n;
@@ -244,36 +290,89 @@ levenshtein_internal(text *s, text *t,
244290
prev[i]=i*del_c;
245291

246292
/* Loop through rows of the notional array */
247-
for (y=VARDATA_ANY(t),j=1;j<n;y++,j++)
293+
for (y=t_data,j=1;j<n;j++)
248294
{
249295
int*temp;
296+
constchar*x=s_data;
297+
inty_char_len=n!=t_bytes+1 ?pg_mblen(y) :1;
250298

251299
/*
252300
* First cell must increment sequentially, as we're on the j'th row of
253301
* the (m+1)x(n+1) array.
254302
*/
255303
curr[0]=j*ins_c;
256304

257-
for (x=VARDATA_ANY(s),i=1;i<m;x++,i++)
305+
/*
306+
* This inner loop is critical to performance, so we include a
307+
* fast-path to handle the (fairly common) case where no multibyte
308+
* characters are in the mix. The fast-path is entitled to assume
309+
* that if s_char_len is not initialized then BOTH strings contain
310+
* only single-byte characters.
311+
*/
312+
if (s_char_len!=NULL)
258313
{
259-
intins;
260-
intdel;
261-
intsub;
262-
263-
/* Calculate costs for probable operations. */
264-
ins=prev[i]+ins_c;/* Insertion*/
265-
del=curr[i-1]+del_c;/* Deletion*/
266-
sub=prev[i-1]+ ((*x==*y) ?0 :sub_c);/* Substitution */
267-
268-
/* Take the one with minimum cost. */
269-
curr[i]=Min(ins,del);
270-
curr[i]=Min(curr[i],sub);
314+
for (i=1;i<m;i++)
315+
{
316+
intins;
317+
intdel;
318+
intsub;
319+
intx_char_len=s_char_len[i-1];
320+
321+
/*
322+
* Calculate costs for insertion, deletion, and substitution.
323+
*
324+
* When calculating cost for substitution, we compare the last
325+
* character of each possibly-multibyte character first,
326+
* because that's enough to rule out most mis-matches. If we
327+
* get past that test, then we compare the lengths and the
328+
* remaining bytes.
329+
*/
330+
ins=prev[i]+ins_c;
331+
del=curr[i-1]+del_c;
332+
if (x[x_char_len-1]==y[y_char_len-1]
333+
&&x_char_len==y_char_len&&
334+
(x_char_len==1||rest_of_char_same(x,y,x_char_len)))
335+
sub=prev[i-1];
336+
else
337+
sub=prev[i-1]+sub_c;
338+
339+
/* Take the one with minimum cost. */
340+
curr[i]=Min(ins,del);
341+
curr[i]=Min(curr[i],sub);
342+
343+
/* Point to next character. */
344+
x+=x_char_len;
345+
}
346+
}
347+
else
348+
{
349+
for (i=1;i<m;i++)
350+
{
351+
intins;
352+
intdel;
353+
intsub;
354+
355+
/* Calculate costs for insertion, deletion, and substitution. */
356+
ins=prev[i]+ins_c;
357+
del=curr[i-1]+del_c;
358+
sub=prev[i-1]+ ((*x==*y) ?0 :sub_c);
359+
360+
/* Take the one with minimum cost. */
361+
curr[i]=Min(ins,del);
362+
curr[i]=Min(curr[i],sub);
363+
364+
/* Point to next character. */
365+
x++;
366+
}
271367
}
272368

273369
/* Swap current row with previous row. */
274370
temp=curr;
275371
curr=prev;
276372
prev=temp;
373+
374+
/* Point to next character. */
375+
y+=y_char_len;
277376
}
278377

279378
/*

‎doc/src/sgml/fuzzystrmatch.sgml‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/fuzzystrmatch.sgml,v 1.6 2010/07/29 19:34:40 petere Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/fuzzystrmatch.sgml,v 1.7 2010/08/02 23:20:23 rhaas Exp $ -->
22

33
<sect1 id="fuzzystrmatch">
44
<title>fuzzystrmatch</title>
@@ -14,8 +14,9 @@
1414

1515
<caution>
1616
<para>
17-
At present, <filename>fuzzystrmatch</> does not work well with
18-
multi-byte encodings (such as UTF-8).
17+
At present, the <function>soundex</>, <function>metaphone</>,
18+
<function>dmetaphone</>, and <function>dmetaphone_alt</> functions do
19+
not work well with multi-byte encodings (such as UTF-8).
1920
</para>
2021
</caution>
2122

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