error safe for casting float8 to other types per pg_cast

select castsource::regtype, casttarget::regtype, castfunc,
castcontext,castmethod, pp.prosrc, pp.proname from pg_cast pc join pg_proc pp on
pp.oid = pc.castfunc and pc.castfunc > 0
and castsource::regtype = 'float8'::regtype
order by castsource::regtype;

    castsource    | casttarget | castfunc | castcontext | castmethod |     prosrc     | proname
------------------+------------+----------+-------------+------------+----------------+---------
 double precision | bigint     |      483 | a           | f          | dtoi8          | int8
 double precision | smallint   |      237 | a           | f          | dtoi2          | int2
 double precision | integer    |      317 | a           | f          | dtoi4          | int4
 double precision | real       |      312 | a           | f          | dtof           | float4
 double precision | numeric    |     1743 | a           | f          | float8_numeric | numeric
(5 rows)

discussion: https://postgr.es/m/CADkLM=fv1JfY4Ufa-jcwwNbjQixNViskQ8jZu3Tz_p656i_4hQ@mail.gmail.com

Author: jianhe-fun

src/backend/utils/adt/float.c

@@ -1199,9 +1199,14 @@ dtof(PG_FUNCTION_ARGS)
 
 	result = (float4) num;
 	if (unlikely(isinf(result)) && !isinf(num))
-		float_overflow_error();
+		ereturn(fcinfo->context, (Datum) 0,
+				errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
+				errmsg("value out of range: overflow"));
+
 	if (unlikely(result == 0.0f) && num != 0.0)
-		float_underflow_error();
+		ereturn(fcinfo->context, (Datum) 0,
+				errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
+				errmsg("value out of range: underflow"));
 
 	PG_RETURN_FLOAT4(result);
 }
@@ -1224,7 +1229,7 @@ dtoi4(PG_FUNCTION_ARGS)
 
 	/* Range check */
 	if (unlikely(isnan(num) || !FLOAT8_FITS_IN_INT32(num)))
-		ereport(ERROR,
+		ereturn(fcinfo->context, (Datum) 0,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("integer out of range")));
 
@@ -1249,7 +1254,7 @@ dtoi2(PG_FUNCTION_ARGS)
 
 	/* Range check */
 	if (unlikely(isnan(num) || !FLOAT8_FITS_IN_INT16(num)))
-		ereport(ERROR,
+		ereturn(fcinfo->context, (Datum) 0,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("smallint out of range")));
 

src/backend/utils/adt/int8.c

@@ -1307,7 +1307,7 @@ dtoi8(PG_FUNCTION_ARGS)
 
 	/* Range check */
 	if (unlikely(isnan(num) || !FLOAT8_FITS_IN_INT64(num)))
-		ereport(ERROR,
+		ereturn(fcinfo->context, (Datum) 0,
 				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
 				 errmsg("bigint out of range")));
 

src/backend/utils/adt/numeric.c

@@ -4560,7 +4560,8 @@ float8_numeric(PG_FUNCTION_ARGS)
 	init_var(&result);
 
 	/* Assume we need not worry about leading/trailing spaces */
-	(void) set_var_from_str(buf, buf, &result, &endptr, NULL);
+	if (!set_var_from_str(buf, buf, &result, &endptr, fcinfo->context))
+		PG_RETURN_NULL();
 
 	res = make_result(&result);