From: Justin Lebar <jlebar@google.com>
Date: Thu, 29 Dec 2016 18:15:34 +0000 (+0000)
Subject: [ADT] Use memcpy for type punning in MathExtras.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=cc13d2043fbaa3b4dc8353a87e86af6515151a08;p=llvm

[ADT] Use memcpy for type punning in MathExtras.

Summary: Previously we type-punned through a union, which is not safe.

Reviewers: rnk

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28161

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290715 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/Support/MathExtras.h b/include/llvm/Support/MathExtras.h
index dd835170c2c..77970f48711 100644
--- a/include/llvm/Support/MathExtras.h
+++ b/include/llvm/Support/MathExtras.h
@@ -547,23 +547,19 @@ inline uint64_t GreatestCommonDivisor64(uint64_t A, uint64_t B) {
 /// BitsToDouble - This function takes a 64-bit integer and returns the bit
 /// equivalent double.
 inline double BitsToDouble(uint64_t Bits) {
-  union {
-    uint64_t L;
-    double D;
-  } T;
-  T.L = Bits;
-  return T.D;
+  double D;
+  static_assert(sizeof(uint64_t) == sizeof(double), "Unexpected type sizes");
+  memcpy(&D, &Bits, sizeof(Bits));
+  return D;
 }
 
 /// BitsToFloat - This function takes a 32-bit integer and returns the bit
 /// equivalent float.
 inline float BitsToFloat(uint32_t Bits) {
-  union {
-    uint32_t I;
-    float F;
-  } T;
-  T.I = Bits;
-  return T.F;
+  float F;
+  static_assert(sizeof(uint32_t) == sizeof(float), "Unexpected type sizes");
+  memcpy(&F, &Bits, sizeof(Bits));
+  return F;
 }
 
 /// DoubleToBits - This function takes a double and returns the bit
@@ -571,12 +567,10 @@ inline float BitsToFloat(uint32_t Bits) {
 /// changes the bits of NaNs on some hosts, notably x86, so this
 /// routine cannot be used if these bits are needed.
 inline uint64_t DoubleToBits(double Double) {
-  union {
-    uint64_t L;
-    double D;
-  } T;
-  T.D = Double;
-  return T.L;
+  uint64_t Bits;
+  static_assert(sizeof(uint64_t) == sizeof(double), "Unexpected type sizes");
+  memcpy(&Bits, &Double, sizeof(Double));
+  return Bits;
 }
 
 /// FloatToBits - This function takes a float and returns the bit
@@ -584,12 +578,10 @@ inline uint64_t DoubleToBits(double Double) {
 /// changes the bits of NaNs on some hosts, notably x86, so this
 /// routine cannot be used if these bits are needed.
 inline uint32_t FloatToBits(float Float) {
-  union {
-    uint32_t I;
-    float F;
-  } T;
-  T.F = Float;
-  return T.I;
+  uint32_t Bits;
+  static_assert(sizeof(uint32_t) == sizeof(float), "Unexpected type sizes");
+  memcpy(&Bits, &Float, sizeof(Float));
+  return Bits;
 }
 
 /// MinAlign - A and B are either alignments or offsets.  Return the minimum