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

src/backend/utils/adt/numeric.c

@@ -4228,11 +4228,13 @@ numericvar_to_int32(const NumericVar *var, int32 *result)
 	if (!numericvar_to_int64(var, &val))
 		return false;
 
+	if (unlikely(val < PG_INT32_MIN) || unlikely(val > PG_INT32_MAX))
+		return false;
+
 	/* Down-convert to int4 */
 	*result = (int32) val;
 
-	/* Test for overflow by reverse-conversion. */
-	return ((int64) *result == val);
+	return true;
 }
 
 Datum
@@ -4312,15 +4314,14 @@ 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 (unlikely(val < PG_INT16_MIN) || unlikely(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);
 }
 
@@ -10147,10 +10148,7 @@ power_var(const NumericVar *base, const 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;
@@ -10158,7 +10156,7 @@ power_var(const NumericVar *base, const 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;
 			}
 		}

src/test/regress/expected/numeric.out

@@ -1154,6 +1154,55 @@ SELECT * FROM fract_only;
 (7 rows)
 
 DROP TABLE fract_only;
+-- Check conversion to integers
+SELECT (-9223372036854775808.5)::int8; -- should fail
+ERROR:  bigint out of range
+SELECT (-9223372036854775808.4)::int8; -- ok
+         int8         
+----------------------
+ -9223372036854775808
+(1 row)
+
+SELECT 9223372036854775807.4::int8; -- ok
+        int8         
+---------------------
+ 9223372036854775807
+(1 row)
+
+SELECT 9223372036854775807.5::int8; -- should fail
+ERROR:  bigint out of range
+SELECT (-2147483648.5)::int4; -- should fail
+ERROR:  integer out of range
+SELECT (-2147483648.4)::int4; -- ok
+    int4     
+-------------
+ -2147483648
+(1 row)
+
+SELECT 2147483647.4::int4; -- ok
+    int4    
+------------
+ 2147483647
+(1 row)
+
+SELECT 2147483647.5::int4; -- should fail
+ERROR:  integer out of range
+SELECT (-32768.5)::int2; -- should fail
+ERROR:  smallint out of range
+SELECT (-32768.4)::int2; -- ok
+  int2  
+--------
+ -32768
+(1 row)
+
+SELECT 32767.4::int2; -- ok
+ int2  
+-------
+ 32767
+(1 row)
+
+SELECT 32767.5::int2; -- should fail
+ERROR:  smallint out of range
 -- Check inf/nan conversion behavior
 SELECT 'NaN'::float8::numeric;
  numeric 
@@ -2365,10 +2414,10 @@ select 1.000000000123 ^ (-2147483648);
  0.7678656556403084
 (1 row)
 
-select 0.9999999999 ^ 23300000000000 = 0 as rounds_to_zero;
+select coalesce(nullif(0.9999999999 ^ 23300000000000, 0), 0) as rounds_to_zero;
  rounds_to_zero 
 ----------------
- t
+              0
 (1 row)
 
 -- cases that used to error out
@@ -2384,10 +2433,10 @@ select 0.5678 ^ (-85);
  782333637740774446257.7719390061997396
 (1 row)
 
-select 0.9999999999 ^ 70000000000000 = 0 as underflows;
+select coalesce(nullif(0.9999999999 ^ 70000000000000, 0), 0) as underflows;
  underflows 
 ------------
- t
+          0
 (1 row)
 
 -- negative base to integer powers
@@ -2557,16 +2606,16 @@ select exp('-inf'::numeric);
    0
 (1 row)
 
-select exp(-5000::numeric) = 0 as rounds_to_zero;
+select coalesce(nullif(exp(-5000::numeric), 0), 0) as rounds_to_zero;
  rounds_to_zero 
 ----------------
- t
+              0
 (1 row)
 
-select exp(-10000::numeric) = 0 as underflows;
+select coalesce(nullif(exp(-10000::numeric), 0), 0) as underflows;
  underflows 
 ------------
- t
+          0
 (1 row)
 
 -- cases that used to generate inaccurate results

src/test/regress/sql/numeric.sql

@@ -773,6 +773,20 @@ INSERT INTO fract_only VALUES (11, '-Inf');	-- should fail
 SELECT * FROM fract_only;
 DROP TABLE fract_only;
 
+-- Check conversion to integers
+SELECT (-9223372036854775808.5)::int8; -- should fail
+SELECT (-9223372036854775808.4)::int8; -- ok
+SELECT 9223372036854775807.4::int8; -- ok
+SELECT 9223372036854775807.5::int8; -- should fail
+SELECT (-2147483648.5)::int4; -- should fail
+SELECT (-2147483648.4)::int4; -- ok
+SELECT 2147483647.4::int4; -- ok
+SELECT 2147483647.5::int4; -- should fail
+SELECT (-32768.5)::int2; -- should fail
+SELECT (-32768.4)::int2; -- ok
+SELECT 32767.4::int2; -- ok
+SELECT 32767.5::int2; -- should fail
+
 -- Check inf/nan conversion behavior
 SELECT 'NaN'::float8::numeric;
 SELECT 'Infinity'::float8::numeric;
@@ -1099,12 +1113,12 @@ select 3.789 ^ 35;
 select 1.2 ^ 345;
 select 0.12 ^ (-20);
 select 1.000000000123 ^ (-2147483648);
-select 0.9999999999 ^ 23300000000000 = 0 as rounds_to_zero;
+select coalesce(nullif(0.9999999999 ^ 23300000000000, 0), 0) as rounds_to_zero;
 
 -- cases that used to error out
 select 0.12 ^ (-25);
 select 0.5678 ^ (-85);
-select 0.9999999999 ^ 70000000000000 = 0 as underflows;
+select coalesce(nullif(0.9999999999 ^ 70000000000000, 0), 0) as underflows;
 
 -- negative base to integer powers
 select (-1.0) ^ 2147483646;
@@ -1154,8 +1168,8 @@ select exp(1.0::numeric(71,70));
 select exp('nan'::numeric);
 select exp('inf'::numeric);
 select exp('-inf'::numeric);
-select exp(-5000::numeric) = 0 as rounds_to_zero;
-select exp(-10000::numeric) = 0 as underflows;
+select coalesce(nullif(exp(-5000::numeric), 0), 0) as rounds_to_zero;
+select coalesce(nullif(exp(-10000::numeric), 0), 0) as underflows;
 
 -- cases that used to generate inaccurate results
 select exp(32.999);