Correct truncation behaviour in WTF::hashInts()

third_party/WebKit/Source/wtf/HashFunctions.h

 /*
  * Copyright (C) 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 93 matching lines @@
   key += ~(key << 27);
   key ^= (key >> 31);
   return static_cast<unsigned>(key);
 }
 
 // Compound integer hash method:
 // http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
 inline unsigned hashInts(unsigned key1, unsigned key2) {
   unsigned shortRandom1 = 277951225;          // A random 32-bit value.
   unsigned shortRandom2 = 95187966;           // A random 32-bit value.
-  uint64_t longRandom = 19248658165952622LL;  // A random 64-bit value.
+  uint64_t longRandom = 19248658165952623LL;  // A random, odd 64-bit value.
 
-  uint64_t product = longRandom * (shortRandom1 * key1 + shortRandom2 * key2);
-  unsigned highBits =
-      static_cast<unsigned>(product >> (sizeof(uint64_t) - sizeof(unsigned)));
+  uint64_t product =
+      longRandom * shortRandom1 * key1 + longRandom * shortRandom2 * key2;
+  unsigned highBits = static_cast<unsigned>(
+      product >> (8 * (sizeof(uint64_t) - sizeof(unsigned))));
   return highBits;
 }
 
 template <typename T>
 struct IntHash {
   static unsigned hash(T key) {
     return hashInt(
         static_cast<typename IntTypes<sizeof(T)>::UnsignedType>(key));
   }
   static bool equal(T a, T b) { return a == b; }
@@ skipping 152 matching lines @@
   using Hash = PairHash<T, U>;
 };
 
 }  // namespace WTF
 
 using WTF::DefaultHash;
 using WTF::IntHash;
 using WTF::PtrHash;
 
 #endif  // WTF_HashFunctions_h