Adjust the integer overflow tests in the numeric code.

Formerly, the numeric code tested whether an integer value of a larger
type would fit in a smaller type by casting it to the smaller type and
then testing if the reverse conversion produced the original value.
That's perfectly fine, except that it caused a test failure on
buildfarm animal castoroides, most likely due to a compiler bug.

Instead, do these tests by comparing against PG_INT16/32_MIN/MAX. That
matches existing code in other places, such as int84(), which is more
widely tested, and so is less likely to go wrong.

While at it, add regression tests covering the numeric-to-int8/4/2
conversions, and adjust the recently added tests to the style of
434ddfb79a (on the v11 branch) to make failures easier to diagnose.

Per buildfarm via Tom Lane, reviewed by Tom Lane.

Discussion: https://postgr.es/m/2394813.1628179479%40sss.pgh.pa.us

1 files changed, 9 insertions, 17 deletions

diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 98574669a2..b485415975 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -2889,7 +2889,6 @@ numeric_int4(PG_FUNCTION_ARGS)
 static int32
 numericvar_to_int32(NumericVar *var)
 {
-	int32		result;
 	int64		val;
 
 	if (!numericvar_to_int64(var, &val))
@@ -2897,16 +2896,13 @@ numericvar_to_int32(NumericVar *var)
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("integer out of range")));
 
-	/* Down-convert to int4 */
-	result = (int32) val;
-
-	/* Test for overflow by reverse-conversion. */
-	if ((int64) result != val)
+	if (val < PG_INT32_MIN || val > PG_INT32_MAX)
 		ereport(ERROR,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("integer out of range")));
 
-	return result;
+	/* Down-convert to int4 */
+	return (int32) val;
 }
 
 Datum
@@ -2994,15 +2990,14 @@ numeric_int2(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("smallint out of range")));
 
-	/* Down-convert to int2 */
-	result = (int16) val;
-
-	/* Test for overflow by reverse-conversion. */
-	if ((int64) result != val)
+	if (val < PG_INT16_MIN || val > PG_INT16_MAX)
 		ereport(ERROR,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("smallint out of range")));
 
+	/* Down-convert to int2 */
+	result = (int16) val;
+
 	PG_RETURN_INT16(result);
 }
 
@@ -7976,10 +7971,7 @@ power_var(NumericVar *base, NumericVar *exp, NumericVar *result)
 
 		if (numericvar_to_int64(exp, &expval64))
 		{
-			int			expval = (int) expval64;
-
-			/* Test for overflow by reverse-conversion. */
-			if ((int64) expval == expval64)
+			if (expval64 >= PG_INT32_MIN && expval64 <= PG_INT32_MAX)
 			{
 				/* Okay, select rscale */
 				rscale = NUMERIC_MIN_SIG_DIGITS;
@@ -7987,7 +7979,7 @@ power_var(NumericVar *base, NumericVar *exp, NumericVar *result)
 				rscale = Max(rscale, NUMERIC_MIN_DISPLAY_SCALE);
 				rscale = Min(rscale, NUMERIC_MAX_DISPLAY_SCALE);
 
-				power_var_int(base, expval, result, rscale);
+				power_var_int(base, (int) expval64, result, rscale);
 				return;
 			}
 		}