From: Mats Kindahl <mats@timescale.com>
Date: Tue, 6 Feb 2024 14:53:53 +0100
Subject: [PATCH v3 2/2] Ensure comparison functions are transitive

There are a few comparison functions to qsort() that are non-transitive
because they can cause an overflow. Fix these functions to instead use
normal comparisons and return -1, 0, or 1 explicitly.
---
 src/backend/access/spgist/spgtextproc.c |  2 +-
 src/backend/utils/cache/relcache.c      |  9 ++++++---
 src/bin/pg_upgrade/function.c           | 10 ++++++----
 src/bin/psql/crosstabview.c             |  5 ++++-
 4 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/backend/access/spgist/spgtextproc.c b/src/backend/access/spgist/spgtextproc.c
index b8fd0c2ad8..e561bde63e 100644
--- a/src/backend/access/spgist/spgtextproc.c
+++ b/src/backend/access/spgist/spgtextproc.c
@@ -325,7 +325,7 @@ cmpNodePtr(const void *a, const void *b)
 	const spgNodePtr *aa = (const spgNodePtr *) a;
 	const spgNodePtr *bb = (const spgNodePtr *) b;
 
-	return aa->c - bb->c;
+	return (aa->c > bb->c) - (aa->c < bb->c);
 }
 
 Datum
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index ac106b40e3..54682a0e60 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -4517,10 +4517,13 @@ AttrDefaultFetch(Relation relation, int ndef)
 static int
 AttrDefaultCmp(const void *a, const void *b)
 {
-	const AttrDefault *ada = (const AttrDefault *) a;
-	const AttrDefault *adb = (const AttrDefault *) b;
+	AttrNumber	ana = ((const AttrDefault *) a)->adnum;
+	AttrNumber	anb = ((const AttrDefault *) b)->adnum;
 
-	return ada->adnum - adb->adnum;
+	/* ensure upcasting approach is transitive */
+	Assert(sizeof(AttrNumber) == 2);
+
+	return (int) ana - (int) anb;
 }
 
 /*
diff --git a/src/bin/pg_upgrade/function.c b/src/bin/pg_upgrade/function.c
index af998f74d3..b421500bbb 100644
--- a/src/bin/pg_upgrade/function.c
+++ b/src/bin/pg_upgrade/function.c
@@ -32,14 +32,16 @@ library_name_compare(const void *p1, const void *p2)
 	int			slen1 = strlen(str1);
 	int			slen2 = strlen(str2);
 	int			cmp = strcmp(str1, str2);
+	int			p1db = ((const LibraryInfo *) p1)->dbnum;
+	int			p2db = ((const LibraryInfo *) p2)->dbnum;
 
 	if (slen1 != slen2)
-		return slen1 - slen2;
+		return (slen1 > slen2) - (slen1 < slen2);
+
 	if (cmp != 0)
 		return cmp;
-	else
-		return ((const LibraryInfo *) p1)->dbnum -
-			((const LibraryInfo *) p2)->dbnum;
+
+	return (p1db > p2db) - (p1db < p2db);
 }
 
 
diff --git a/src/bin/psql/crosstabview.c b/src/bin/psql/crosstabview.c
index c6116b7238..7660f0ed4b 100644
--- a/src/bin/psql/crosstabview.c
+++ b/src/bin/psql/crosstabview.c
@@ -709,5 +709,8 @@ pivotFieldCompare(const void *a, const void *b)
 static int
 rankCompare(const void *a, const void *b)
 {
-	return *((const int *) a) - *((const int *) b);
+	const int	an = *(const int *) a;
+	const int	bn = *(const int *) b;
+
+	return (an > bn) - (an < bn);
 }
-- 
2.25.1


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