From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 20 Oct 2023 17:40:15 +0000 (-0400)
Subject: Dodge a compiler bug affecting timetz_zone/timetz_izone.
X-Git-Tag: REL_11_22~25
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e98f47d570a22e7aaaf71b79d6ce6852701bbd8d;p=thirdparty%2Fpostgresql.git

Dodge a compiler bug affecting timetz_zone/timetz_izone.

This avoids a compiler bug occurring in AIX's xlc, even in pretty
late-model revisions.  Buildfarm testing has now confirmed that
only 64-bit xlc is affected.  Although we are contemplating
dropping support for xlc in v17, it's still supported in the
back branches, so we need this fix.

Back-patch of code changes from HEAD commit 19fa97731.
(The test cases were already back-patched, in 4a427b82c et al.)

Discussion: https://postgr.es/m/CA+hUKGK=DOC+hE-62FKfZy=Ybt5uLkrg3zCZD-jFykM-iPn8yw@mail.gmail.com
---

diff --git a/src/backend/utils/adt/date.c b/src/backend/utils/adt/date.c
index 986fadcdb11..112e74d7afc 100644
--- a/src/backend/utils/adt/date.c
+++ b/src/backend/utils/adt/date.c
@@ -2877,10 +2877,11 @@ timetz_zone(PG_FUNCTION_ARGS)
 	result = (TimeTzADT *) palloc(sizeof(TimeTzADT));
 
 	result->time = t->time + (t->zone - tz) * USECS_PER_SEC;
+	/* C99 modulo has the wrong sign convention for negative input */
 	while (result->time < INT64CONST(0))
 		result->time += USECS_PER_DAY;
-	while (result->time >= USECS_PER_DAY)
-		result->time -= USECS_PER_DAY;
+	if (result->time >= USECS_PER_DAY)
+		result->time %= USECS_PER_DAY;
 
 	result->zone = tz;
 
@@ -2910,10 +2911,11 @@ timetz_izone(PG_FUNCTION_ARGS)
 	result = (TimeTzADT *) palloc(sizeof(TimeTzADT));
 
 	result->time = time->time + (time->zone - tz) * USECS_PER_SEC;
+	/* C99 modulo has the wrong sign convention for negative input */
 	while (result->time < INT64CONST(0))
 		result->time += USECS_PER_DAY;
-	while (result->time >= USECS_PER_DAY)
-		result->time -= USECS_PER_DAY;
+	if (result->time >= USECS_PER_DAY)
+		result->time %= USECS_PER_DAY;
 
 	result->zone = tz;