From edc8d6fa7cd9e552fc4d33f732af0ee22764e086 Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@2ndquadrant.com>
Date: Thu, 26 Jul 2018 16:16:38 +0200
Subject: [PATCH 5/6] Check for float -0 after multiplications and divisions

Discussion: https://www.postgresql.org/message-id/CAE2gYzxF7-5djV6-cEvqQu-fNsnt%3DEqbOURx7ZDg%2BVv6ZMTWbg%40mail.gmail.com
---
 src/include/utils/float.h | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/include/utils/float.h b/src/include/utils/float.h
index 0e8483c930..e359d8a3d4 100644
--- a/src/include/utils/float.h
+++ b/src/include/utils/float.h
@@ -216,11 +216,14 @@ float8_mi(const float8 val1, const float8 val2)
 static inline float4
 float4_mul(const float4 val1, const float4 val2)
 {
+	const bool	zero_is_valid = val1 == 0.0f || val2 == 0.0f;
 	float4		result;
 
 	result = val1 * val2;
-	check_float4_val(result, isinf(val1) || isinf(val2),
-					 val1 == 0.0f || val2 == 0.0f);
+	check_float4_val(result, isinf(val1) || isinf(val2), zero_is_valid);
+
+	if (zero_is_valid && unlikely(result == -0.0f))
+		result = 0.0f;
 
 	return result;
 }
@@ -228,11 +231,14 @@ float4_mul(const float4 val1, const float4 val2)
 static inline float8
 float8_mul(const float8 val1, const float8 val2)
 {
+	const bool	zero_is_valid = val1 == 0.0 || val2 == 0.0;
 	float8		result;
 
 	result = val1 * val2;
-	check_float8_val(result, isinf(val1) || isinf(val2),
-					 val1 == 0.0 || val2 == 0.0);
+	check_float8_val(result, isinf(val1) || isinf(val2), zero_is_valid);
+
+	if (zero_is_valid && unlikely(result == -0.0))
+		result = 0.0;
 
 	return result;
 }
@@ -240,6 +246,7 @@ float8_mul(const float8 val1, const float8 val2)
 static inline float4
 float4_div(const float4 val1, const float4 val2)
 {
+	const bool	zero_is_valid = val1 == 0.0f;
 	float4		result;
 
 	if (val2 == 0.0f)
@@ -248,7 +255,10 @@ float4_div(const float4 val1, const float4 val2)
 				 errmsg("division by zero")));
 
 	result = val1 / val2;
-	check_float4_val(result, isinf(val1) || isinf(val2), val1 == 0.0f);
+	check_float4_val(result, isinf(val1) || isinf(val2), zero_is_valid);
+
+	if (zero_is_valid && unlikely(result == -0.0f))
+		result = 0.0f;
 
 	return result;
 }
@@ -256,6 +266,7 @@ float4_div(const float4 val1, const float4 val2)
 static inline float8
 float8_div(const float8 val1, const float8 val2)
 {
+	const bool	zero_is_valid = val1 == 0.0;
 	float8		result;
 
 	if (val2 == 0.0)
@@ -264,7 +275,10 @@ float8_div(const float8 val1, const float8 val2)
 				 errmsg("division by zero")));
 
 	result = val1 / val2;
-	check_float8_val(result, isinf(val1) || isinf(val2), val1 == 0.0);
+	check_float8_val(result, isinf(val1) || isinf(val2), zero_is_valid);
+
+	if (zero_is_valid && unlikely(result == -0.0))
+		result = 0.0;
 
 	return result;
 }
-- 
2.13.6