From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 13 Feb 2013 19:07:22 +0000 (-0500)
Subject: Fix contrib/pg_trgm's similarity() function for trigram-free strings.
X-Git-Tag: REL9_0_13~26
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=04d7fa5e31f094bd1d87e2da93ba1786a882884f;p=postgresql

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.
---

diff --git a/contrib/pg_trgm/expected/pg_trgm.out b/contrib/pg_trgm/expected/pg_trgm.out
index 9838534729..641e8cecf6 100644
--- a/contrib/pg_trgm/expected/pg_trgm.out
+++ b/contrib/pg_trgm/expected/pg_trgm.out
@@ -59,6 +59,12 @@ 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;
diff --git a/contrib/pg_trgm/sql/pg_trgm.sql b/contrib/pg_trgm/sql/pg_trgm.sql
index 13045827ac..1bcf2c9146 100644
--- a/contrib/pg_trgm/sql/pg_trgm.sql
+++ b/contrib/pg_trgm/sql/pg_trgm.sql
@@ -19,6 +19,8 @@ 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
diff --git a/contrib/pg_trgm/trgm_op.c b/contrib/pg_trgm/trgm_op.c
index 19b6747d68..30965f818c 100644
--- a/contrib/pg_trgm/trgm_op.c
+++ b/contrib/pg_trgm/trgm_op.c
@@ -311,6 +311,10 @@ 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);
@@ -328,9 +332,9 @@ 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
 
 }