Make floating-point "NaN / 0" return NaN instead of raising an error.

This is more consistent with the IEEE 754 spec and our treatment of
NaNs elsewhere; in particular, the case has always acted that way in
"numeric" arithmetic.

Noted by Dean Rasheed.

Discussion: https://postgr.es/m/3421746.1594927785@sss.pgh.pa.us

src/include/utils/float.h

@@ -222,7 +222,7 @@ float4_div(const float4 val1, const float4 val2)
 {
 	float4		result;
 
-	if (unlikely(val2 == 0.0f))
+	if (unlikely(val2 == 0.0f) && !isnan(val1))
 		float_zero_divide_error();
 	result = val1 / val2;
 	if (unlikely(isinf(result)) && !isinf(val1) && !isinf(val2))
@@ -238,7 +238,7 @@ float8_div(const float8 val1, const float8 val2)
 {
 	float8		result;
 
-	if (unlikely(val2 == 0.0))
+	if (unlikely(val2 == 0.0) && !isnan(val1))
 		float_zero_divide_error();
 	result = val1 / val2;
 	if (unlikely(isinf(result)) && !isinf(val1) && !isinf(val2))

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

@@ -143,6 +143,12 @@ SELECT 'nan'::float4 / 'nan'::float4;
       NaN
 (1 row)
 
+SELECT 'nan'::float4 / '0'::float4;
+ ?column? 
+----------
+      NaN
+(1 row)
+
 SELECT 'nan'::numeric::float4;
  float4 
 --------

src/test/regress/expected/float4.out

@@ -143,6 +143,12 @@ SELECT 'nan'::float4 / 'nan'::float4;
       NaN
 (1 row)
 
+SELECT 'nan'::float4 / '0'::float4;
+ ?column? 
+----------
+      NaN
+(1 row)
+
 SELECT 'nan'::numeric::float4;
  float4 
 --------

src/test/regress/expected/float8.out

@@ -126,6 +126,12 @@ SELECT 'nan'::float8 / 'nan'::float8;
       NaN
 (1 row)
 
+SELECT 'nan'::float8 / '0'::float8;
+ ?column? 
+----------
+      NaN
+(1 row)
+
 SELECT 'nan'::numeric::float8;
  float8 
 --------

src/test/regress/sql/float4.sql

@@ -50,6 +50,7 @@ SELECT ' INFINITY    x'::float4;
 SELECT 'Infinity'::float4 + 100.0;
 SELECT 'Infinity'::float4 / 'Infinity'::float4;
 SELECT 'nan'::float4 / 'nan'::float4;
+SELECT 'nan'::float4 / '0'::float4;
 SELECT 'nan'::numeric::float4;
 
 SELECT '' AS five, * FROM FLOAT4_TBL;

src/test/regress/sql/float8.sql

@@ -43,6 +43,7 @@ SELECT ' INFINITY    x'::float8;
 SELECT 'Infinity'::float8 + 100.0;
 SELECT 'Infinity'::float8 / 'Infinity'::float8;
 SELECT 'nan'::float8 / 'nan'::float8;
+SELECT 'nan'::float8 / '0'::float8;
 SELECT 'nan'::numeric::float8;
 
 SELECT '' AS five, * FROM FLOAT8_TBL;