From f4d63ff07d92c6479ffe4b22787e5d6cae24eff7 Mon Sep 17 00:00:00 2001
From: Lioncash <mathew1800@gmail.com>
Date: Mon, 1 Apr 2019 19:51:45 -0400
Subject: [PATCH] common/fp/op/FPRecipExponent: Prevent undefined behavior from
 shifting a negative value

Due to promotion rules (types < int, even if unsigned, get promoted to
int when arithmetic is performed on them), this is a potential spot for
undefined behavior.
---
 src/common/fp/op/FPRecipExponent.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/common/fp/op/FPRecipExponent.cpp b/src/common/fp/op/FPRecipExponent.cpp
index 4e0224e7..eafad6a9 100644
--- a/src/common/fp/op/FPRecipExponent.cpp
+++ b/src/common/fp/op/FPRecipExponent.cpp
@@ -48,8 +48,9 @@ FPT FPRecipExponent(FPT op, FPCR fpcr, FPSR& fpsr) {
     }
 
     // Infinities and normals
-    const auto negated_exponent = (~exponent << FPInfo<FPT>::explicit_mantissa_width) & FPInfo<FPT>::exponent_mask;
-    return FPT(sign_bits | negated_exponent);
+    const FPT negated_exponent = FPT(~exponent);
+    const FPT adjusted_exponent = FPT(negated_exponent << FPInfo<FPT>::explicit_mantissa_width) & FPInfo<FPT>::exponent_mask;
+    return FPT(sign_bits | adjusted_exponent);
 }
 
 template u16 FPRecipExponent<u16>(u16 op, FPCR fpcr, FPSR& fpsr);