Fix longstanding error in contrib/intarray's int[] & int[] operator.

The array intersection code would give wrong results if the first entry of
the correct output array would be "1".  (I think only this value could be
at risk, since the previous word would always be a lower-bound entry with
that fixed value.)

Problem spotted by Julien Rouhaud, initial patch by Guillaume Lelarge,
cosmetic improvements by me.

3 files changed, 16 insertions, 6 deletions

diff --git a/contrib/intarray/_int_tool.c b/contrib/intarray/_int_tool.c
index 8c0ec29c31b..780b28bc3f9 100644
--- a/contrib/intarray/_int_tool.c
+++ b/contrib/intarray/_int_tool.c
@@ -146,7 +146,8 @@ inner_int_inter(ArrayType *a, ArrayType *b)
 			   *db,
 			   *dr;
 	int			i,
-				j;
+				j,
+				k;
 
 	CHECKARRVALID(a);
 	CHECKARRVALID(b);
@@ -161,27 +162,29 @@ inner_int_inter(ArrayType *a, ArrayType *b)
 	r = new_intArrayType(Min(na, nb));
 	dr = ARRPTR(r);
 
-	i = j = 0;
+	i = j = k = 0;
 	while (i < na && j < nb)
+	{
 		if (da[i] < db[j])
 			i++;
 		else if (da[i] == db[j])
 		{
-			if (i + j == 0 || (i + j > 0 && *(dr - 1) != db[j]))
-				*dr++ = db[j];
+			if (k == 0 || dr[k - 1] != db[j])
+				dr[k++] = db[j];
 			i++;
 			j++;
 		}
 		else
 			j++;
+	}
 
-	if ((dr - ARRPTR(r)) == 0)
+	if (k == 0)
 	{
 		pfree(r);
 		return new_intArrayType(0);
 	}
 	else
-		return resize_intArrayType(r, dr - ARRPTR(r));
+		return resize_intArrayType(r, k);
 }
 
 void
diff --git a/contrib/intarray/expected/_int.out b/contrib/intarray/expected/_int.out
index 596439d3149..ab28ad33de1 100644
--- a/contrib/intarray/expected/_int.out
+++ b/contrib/intarray/expected/_int.out
@@ -143,6 +143,12 @@ SELECT '{123,623,445}'::int[] & '{1623,623}';
  {623}
 (1 row)
 
+SELECT '{-1,3,1}'::int[] & '{1,2}';
+ ?column? 
+----------
+ {1}
+(1 row)
+
 --test query_int
 SELECT '1'::query_int;
  query_int 
diff --git a/contrib/intarray/sql/_int.sql b/contrib/intarray/sql/_int.sql
index 1588e3b5145..d020c5fa8e3 100644
--- a/contrib/intarray/sql/_int.sql
+++ b/contrib/intarray/sql/_int.sql
@@ -32,6 +32,7 @@ SELECT '{123,623,445}'::int[] | 623;
 SELECT '{123,623,445}'::int[] | 1623;
 SELECT '{123,623,445}'::int[] | '{1623,623}';
 SELECT '{123,623,445}'::int[] & '{1623,623}';
+SELECT '{-1,3,1}'::int[] & '{1,2}';
 
 
 --test query_int