From 58ae15dcd21150f159766f2757fd27f7c709d226 Mon Sep 17 00:00:00 2001
From: "Evgeniy A. Dushistov" <dushistov@mail.ru>
Date: Tue, 20 Apr 2021 15:09:31 +0300
Subject: [PATCH] Fix reinterpret_cast UB for base::AlmostEqualULPs

Usage of reinterpret_cast here break strict aliasing rules,
so this is undefined behaviour. gcc reports:
dereferencing type-punned pointer will break strict-aliasing rules
[-Wstrict-aliasing]

I checked generated assembly, and in clang case `AlmostEqualULPs`
generates the same code before and after my patch. So it should not be
any speed regression after this UB fix.

Signed-off-by: Evgeniy A. Dushistov <dushistov@mail.ru>
---
 base/math.hpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/base/math.hpp b/base/math.hpp
index ecf60e09fb..616527e839 100644
--- a/base/math.hpp
+++ b/base/math.hpp
@@ -5,6 +5,7 @@
 #include <algorithm>
 #include <climits>
 #include <cmath>
+#include <cstring>
 #include <functional>
 #include <limits>
 #include <type_traits>
@@ -55,10 +56,10 @@ bool AlmostEqualULPs(Float x, Float y, unsigned int maxULPs = 256)
   int const bits = CHAR_BIT * sizeof(Float);
   typedef typename boost::int_t<bits>::exact IntType;
   typedef typename boost::uint_t<bits>::exact UIntType;
-
-  IntType xInt = *reinterpret_cast<IntType const *>(&x);
-  IntType yInt = *reinterpret_cast<IntType const *>(&y);
-
+  IntType xInt, yInt;
+  static_assert(sizeof(xInt) == sizeof(x), "bit_cast impossible");
+  std::memcpy(&xInt, &x, sizeof(x));
+  std::memcpy(&yInt, &y, sizeof(y));
   // Make xInt and yInt lexicographically ordered as a twos-complement int
   IntType const highestBit = IntType(1) << (bits - 1);
   if (xInt < 0)