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Fix contrib/pg_trgm's similarity() function for trigram-free strings.

Cases such as similarity('', '') produced a NaN result due to computing
0/0.  Per discussion, make it return zero instead.

This appears to be the basic cause of bug #7867 from Michele Baravalle,
although it remains unclear why her installation doesn't think Cyrillic
letters are letters.

Back-patch to all active branches.
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1 parent cd89965 commit 9728eda7925b6d42621b38c48e91ef9ab8d90cbc @tglsfdc tglsfdc committed Feb 13, 2013
Showing with 14 additions and 2 deletions.
  1. +6 −0 contrib/pg_trgm/expected/pg_trgm.out
  2. +2 −0 contrib/pg_trgm/sql/pg_trgm.sql
  3. +6 −2 contrib/pg_trgm/trgm_op.c
View
6 contrib/pg_trgm/expected/pg_trgm.out
@@ -53,6 +53,12 @@ select similarity('wow',' WOW ');
1
(1 row)
+select similarity('---', '####---');
+ similarity
+------------
+ 0
+(1 row)
+
CREATE TABLE test_trgm(t text);
\copy test_trgm from 'data/trgm.data
select t,similarity(t,'qwertyu0988') as sml from test_trgm where t % 'qwertyu0988' order by sml desc, t;
View
2 contrib/pg_trgm/sql/pg_trgm.sql
@@ -11,6 +11,8 @@ select show_trgm('a b C0*%^');
select similarity('wow','WOWa ');
select similarity('wow',' WOW ');
+select similarity('---', '####---');
+
CREATE TABLE test_trgm(t text);
\copy test_trgm from 'data/trgm.data
View
8 contrib/pg_trgm/trgm_op.c
@@ -553,6 +553,10 @@ cnt_sml(TRGM *trg1, TRGM *trg2)
len1 = ARRNELEM(trg1);
len2 = ARRNELEM(trg2);
+ /* explicit test is needed to avoid 0/0 division when both lengths are 0 */
+ if (len1 <= 0 || len2 <= 0)
+ return (float4) 0.0;
+
while (ptr1 - GETARR(trg1) < len1 && ptr2 - GETARR(trg2) < len2)
{
int res = CMPTRGM(ptr1, ptr2);
@@ -570,9 +574,9 @@ cnt_sml(TRGM *trg1, TRGM *trg2)
}
#ifdef DIVUNION
- return ((((float4) count) / ((float4) (len1 + len2 - count))));
+ return ((float4) count) / ((float4) (len1 + len2 - count));
#else
- return (((float) count) / ((float) ((len1 > len2) ? len1 : len2)));
+ return ((float4) count) / ((float4) ((len1 > len2) ? len1 : len2));
#endif
}

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