[libc-commits] [libc] [libc] Fix undefined behavior in expxf16.h (PR #112734)

[via libc-commits]

https://github.com/overmighty created https://github.com/llvm/llvm-project/pull/112734

Fixes the left-shifting of potentially negative signed integers.


>From e1a252c65fa0037f322e0fd8eb08f5a403db48a2 Mon Sep 17 00:00:00 2001
From: OverMighty <its.overmighty at gmail.com>
Date: Thu, 17 Oct 2024 17:45:07 +0200
Subject: [PATCH] [libc] Fix undefined behavior in expxf16.h

Fixes the left-shifting of potentially negative signed integers.
---
 libc/src/math/generic/expxf16.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libc/src/math/generic/expxf16.h b/libc/src/math/generic/expxf16.h
index 8de329bd2ab07f..aba99a2914b41d 100644
--- a/libc/src/math/generic/expxf16.h
+++ b/libc/src/math/generic/expxf16.h
@@ -108,8 +108,8 @@ LIBC_INLINE ExpRangeReduction exp2_range_reduction(float16 x) {
   float xf = x;
   float kf = fputil::nearest_integer(xf * 0x1.0p+3f);
   int x_hi_mid = static_cast<int>(kf);
-  int x_hi = x_hi_mid >> 3;
-  int x_mid = x_hi_mid & 0x7;
+  unsigned x_hi = static_cast<unsigned>(x_hi_mid) >> 3;
+  unsigned x_mid = static_cast<unsigned>(x_hi_mid) & 0x7;
   // lo = x - (hi + mid) = round(x * 2^3) * (-2^(-3)) + x
   float lo = fputil::multiply_add(kf, -0x1.0p-3f, xf);
 
@@ -155,8 +155,8 @@ LIBC_INLINE ExpRangeReduction exp10_range_reduction(float16 x) {
   float xf = x;
   float kf = fputil::nearest_integer(xf * (LOG2F_10 * 0x1.0p+3f));
   int x_hi_mid = static_cast<int>(kf);
-  int x_hi = x_hi_mid >> 3;
-  int x_mid = x_hi_mid & 0x7;
+  unsigned x_hi = static_cast<unsigned>(x_hi_mid) >> 3;
+  unsigned x_mid = static_cast<unsigned>(x_hi_mid) & 0x7;
   // lo = x - (hi + mid) = round(x * 2^3 * log2(10)) * log10(2) * (-2^(-3)) + x
   float lo = fputil::multiply_add(kf, LOG10F_2 * -0x1.0p-3f, xf);