Remove underflow error in float division with infinite divisor.

float4_div and float8_div correctly produced zero for zero divided
by infinity, but threw an underflow error for nonzero finite values
divided by infinity.  This seems wrong; at the very least it's
inconsistent with the behavior recently implemented for numeric
infinities.  Remove the error and allow zero to be returned.

This patch also removes a useless isinf() test from the overflow
checks in these functions (non-Inf divided by Inf can't produce Inf).

Extracted from a larger patch; this seems significant outside the
context of geometric operators, so it deserves its own commit.

Kyotaro Horiguchi

Discussion: https://postgr.es/m/CAGf+fX70rWFOk5cd00uMfa__0yP+vtQg5ck7c2Onb-Yczp0URA@mail.gmail.com

src/include/utils/float.h

@@ -225,9 +225,9 @@ float4_div(const float4 val1, const float4 val2)
 	if (unlikely(val2 == 0.0f) && !isnan(val1))
 		float_zero_divide_error();
 	result = val1 / val2;
-	if (unlikely(isinf(result)) && !isinf(val1) && !isinf(val2))
+	if (unlikely(isinf(result)) && !isinf(val1))
 		float_overflow_error();
-	if (unlikely(result == 0.0f) && val1 != 0.0f)
+	if (unlikely(result == 0.0f) && val1 != 0.0f && !isinf(val2))
 		float_underflow_error();
 
 	return result;
@@ -241,9 +241,9 @@ float8_div(const float8 val1, const float8 val2)
 	if (unlikely(val2 == 0.0) && !isnan(val1))
 		float_zero_divide_error();
 	result = val1 / val2;
-	if (unlikely(isinf(result)) && !isinf(val1) && !isinf(val2))
+	if (unlikely(isinf(result)) && !isinf(val1))
 		float_overflow_error();
-	if (unlikely(result == 0.0) && val1 != 0.0)
+	if (unlikely(result == 0.0) && val1 != 0.0 && !isinf(val2))
 		float_underflow_error();
 
 	return result;

src/test/regress/expected/float4-misrounded-input.out

@@ -137,6 +137,12 @@ SELECT 'Infinity'::float4 / 'Infinity'::float4;
       NaN
 (1 row)
 
+SELECT '42'::float4 / 'Infinity'::float4;
+ ?column? 
+----------
+        0
+(1 row)
+
 SELECT 'nan'::float4 / 'nan'::float4;
  ?column? 
 ----------

src/test/regress/expected/float4.out

@@ -137,6 +137,12 @@ SELECT 'Infinity'::float4 / 'Infinity'::float4;
       NaN
 (1 row)
 
+SELECT '42'::float4 / 'Infinity'::float4;
+ ?column? 
+----------
+        0
+(1 row)
+
 SELECT 'nan'::float4 / 'nan'::float4;
  ?column? 
 ----------

src/test/regress/expected/float8.out

@@ -120,6 +120,12 @@ SELECT 'Infinity'::float8 / 'Infinity'::float8;
       NaN
 (1 row)
 
+SELECT '42'::float8 / 'Infinity'::float8;
+ ?column? 
+----------
+        0
+(1 row)
+
 SELECT 'nan'::float8 / 'nan'::float8;
  ?column? 
 ----------

src/test/regress/sql/float4.sql

@@ -49,6 +49,7 @@ SELECT ' INFINITY    x'::float4;
 
 SELECT 'Infinity'::float4 + 100.0;
 SELECT 'Infinity'::float4 / 'Infinity'::float4;
+SELECT '42'::float4 / 'Infinity'::float4;
 SELECT 'nan'::float4 / 'nan'::float4;
 SELECT 'nan'::float4 / '0'::float4;
 SELECT 'nan'::numeric::float4;

src/test/regress/sql/float8.sql

@@ -42,6 +42,7 @@ SELECT ' INFINITY    x'::float8;
 
 SELECT 'Infinity'::float8 + 100.0;
 SELECT 'Infinity'::float8 / 'Infinity'::float8;
+SELECT '42'::float8 / 'Infinity'::float8;
 SELECT 'nan'::float8 / 'nan'::float8;
 SELECT 'nan'::float8 / '0'::float8;
 SELECT 'nan'::numeric::float8;