From a60f7228380989d04000bda7e519edc2ab901784 Mon Sep 17 00:00:00 2001
From: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Date: Sat, 22 Jul 2023 20:50:41 -0300
Subject: [PATCH] math/big: handle additional edge cases for Rat

New special cases have been added to the Rat testcases.
Updated the function quotToFloat32/64 to check for zero
as well when determining if the value is infinite. This
change ensures that the exact flag is correctly set for
these edge cases, preventing test failures.

Thanks Johan Jansons (@jupj) for the proposed fix on
the ticket description.

Fixes: #56164
---
 src/math/big/rat.go          | 4 ++--
 src/math/big/ratconv_test.go | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/math/big/rat.go b/src/math/big/rat.go
index 700a643265..75a3e39b8c 100644
--- a/src/math/big/rat.go
+++ b/src/math/big/rat.go
@@ -162,7 +162,7 @@ func quotToFloat32(a, b nat) (f float32, exact bool) {
 	mantissa >>= 1 // discard rounding bit.  Mantissa now scaled by 1<<Msize1.
 
 	f = float32(math.Ldexp(float64(mantissa), exp-Msize1))
-	if math.IsInf(float64(f), 0) {
+	if math.IsInf(float64(f), 0) || f == 0 {
 		exact = false
 	}
 	return
@@ -260,7 +260,7 @@ func quotToFloat64(a, b nat) (f float64, exact bool) {
 	mantissa >>= 1 // discard rounding bit.  Mantissa now scaled by 1<<Msize1.
 
 	f = math.Ldexp(float64(mantissa), exp-Msize1)
-	if math.IsInf(f, 0) {
+	if math.IsInf(f, 0) || f == 0 {
 		exact = false
 	}
 	return
diff --git a/src/math/big/ratconv_test.go b/src/math/big/ratconv_test.go
index 45a35608f4..d2fa9db0be 100644
--- a/src/math/big/ratconv_test.go
+++ b/src/math/big/ratconv_test.go
@@ -466,6 +466,11 @@ var float64inputs = []string{
 	"-1152921504606846977", // -(1<<60 + 1)
 
 	"1/3",
+
+	"170141183460469231731687303715884105728p-48317",
+	"0000000000000000000000000000031768211457p-9818716",
+	"00000000000000000000000000000000000000000000000000000000001662320182p-801401",
+	"818p-8818873",
 }
 
 // isFinite reports whether f represents a finite rational value.