Remove dependence on -fwrapv semantics in a few places.

This commit attempts to update a few places, such as the money,
numeric, and timestamp types, to no longer rely on signed integer
wrapping for correctness.  This is intended to move us closer
towards removing -fwrapv, which may enable some compiler
optimizations.  However, there is presently no plan to actually
remove that compiler option in the near future.

Besides using some of the existing overflow-aware routines in
int.h, this commit introduces and makes use of some new ones.
Specifically, it adds functions that accept a signed integer and
return its absolute value as an unsigned integer with the same
width (e.g., pg_abs_s64()).  It also adds functions that accept an
unsigned integer, store the result of negating that integer in a
signed integer with the same width, and return whether the negation
overflowed (e.g., pg_neg_u64_overflow()).

Finally, this commit adds a couple of tests for timestamps near
POSTGRES_EPOCH_JDATE.

Author: Joseph Koshakow
Reviewed-by: Tom Lane, Heikki Linnakangas, Jian He
Discussion: https://postgr.es/m/CAAvxfHdBPOyEGS7s%2Bxf4iaW0-cgiq25jpYdWBqQqvLtLe_t6tw%40mail.gmail.com

1 files changed, 4 insertions, 24 deletions

diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index 69fe7860ede..43800addf48 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -618,19 +618,8 @@ make_timestamp_internal(int year, int month, int day,
 	time = (((hour * MINS_PER_HOUR + min) * SECS_PER_MINUTE)
 			* USECS_PER_SEC) + (int64) rint(sec * USECS_PER_SEC);
 
-	result = date * USECS_PER_DAY + time;
-	/* check for major overflow */
-	if ((result - time) / USECS_PER_DAY != date)
-		ereport(ERROR,
-				(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-				 errmsg("timestamp out of range: %d-%02d-%02d %d:%02d:%02g",
-						year, month, day,
-						hour, min, sec)));
-
-	/* check for just-barely overflow (okay except time-of-day wraps) */
-	/* caution: we want to allow 1999-12-31 24:00:00 */
-	if ((result < 0 && date > 0) ||
-		(result > 0 && date < -1))
+	if (unlikely(pg_mul_s64_overflow(date, USECS_PER_DAY, &result) ||
+				 pg_add_s64_overflow(result, time, &result)))
 		ereport(ERROR,
 				(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
 				 errmsg("timestamp out of range: %d-%02d-%02d %d:%02d:%02g",
@@ -2010,17 +1999,8 @@ tm2timestamp(struct pg_tm *tm, fsec_t fsec, int *tzp, Timestamp *result)
 	date = date2j(tm->tm_year, tm->tm_mon, tm->tm_mday) - POSTGRES_EPOCH_JDATE;
 	time = time2t(tm->tm_hour, tm->tm_min, tm->tm_sec, fsec);
 
-	*result = date * USECS_PER_DAY + time;
-	/* check for major overflow */
-	if ((*result - time) / USECS_PER_DAY != date)
-	{
-		*result = 0;			/* keep compiler quiet */
-		return -1;
-	}
-	/* check for just-barely overflow (okay except time-of-day wraps) */
-	/* caution: we want to allow 1999-12-31 24:00:00 */
-	if ((*result < 0 && date > 0) ||
-		(*result > 0 && date < -1))
+	if (unlikely(pg_mul_s64_overflow(date, USECS_PER_DAY, result) ||
+				 pg_add_s64_overflow(*result, time, result)))
 	{
 		*result = 0;			/* keep compiler quiet */
 		return -1;