From b0e1a4bd5e1d2057d0ddab9b93f2cccb538989dc Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 16 Feb 2012 20:00:34 -0500
Subject: [PATCH] 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.
---
 contrib/intarray/_int_tool.c       | 15 +++++++++------
 contrib/intarray/expected/_int.out |  6 ++++++
 contrib/intarray/sql/_int.sql      |  1 +
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/contrib/intarray/_int_tool.c b/contrib/intarray/_int_tool.c
index fead4ff30dc..1c6b7301a2b 100644
--- a/contrib/intarray/_int_tool.c
+++ b/contrib/intarray/_int_tool.c
@@ -139,7 +139,8 @@ inner_int_inter(ArrayType *a, ArrayType *b)
 			   *db,
 			   *dr;
 	int			i,
-				j;
+				j,
+				k;
 
 	CHECKARRVALID(a);
 	CHECKARRVALID(b);
@@ -154,27 +155,29 @@ 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