[libc-commits] [libc] 87645e9 - [libc][math][c23] Fix undefined behavior in expxf16.h (#112734)

[via libc-commits]

Author: OverMighty
Date: 2024-10-17T18:37:58+02:00
New Revision: 87645e920528802fb1864e159da3d2be1b733432

URL: https://github.com/llvm/llvm-project/commit/87645e920528802fb1864e159da3d2be1b733432
DIFF: https://github.com/llvm/llvm-project/commit/87645e920528802fb1864e159da3d2be1b733432.diff

LOG: [libc][math][c23] Fix undefined behavior in expxf16.h (#112734)

Fixes the left-shifting of potentially negative signed integers.

Added: 
    

Modified: 
    libc/src/math/generic/expxf16.h

Removed: 
    


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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);