Extract pair hash functions so that they can be re-used outside of hash tables

base/containers/hash_tables.h

Index: base/containers/hash_tables.h
diff --git a/base/containers/hash_tables.h b/base/containers/hash_tables.h
index 0615e0dd33775758d674f4c392dd059043f117fd..2a2b52f9da64e14c7bf3888164be35f37c601dc5 100644
--- a/base/containers/hash_tables.h
+++ b/base/containers/hash_tables.h
@@ -118,36 +118,6 @@ using BASE_HASH_NAMESPACE::hash_map;
 using BASE_HASH_NAMESPACE::hash_multimap;
 using BASE_HASH_NAMESPACE::hash_multiset;
 using BASE_HASH_NAMESPACE::hash_set;
-}
-
-
-// Implement methods for hashing a pair of integers, so they can be used as
-// keys in STL containers.
-
-#if defined(COMPILER_MSVC)
-
-#define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
-    template<> \
-    inline std::size_t hash_value<std::pair<type1, type2> >( \
-        const std::pair<type1, type2>& value)
-
-#define DEFINE_PAIR_HASH_FUNCTION_END()
-
-#elif defined(COMPILER_GCC)
-
-#define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
-    template<> \
-    struct hash<std::pair<type1, type2> > { \
-      std::size_t operator()(std::pair<type1, type2> value) const
-
-#define DEFINE_PAIR_HASH_FUNCTION_END() \
-    };
-
-#else
-#error define DEFINE_PAIR_HASH_FUNCTION_START for your compiler
-#endif  // COMPILER
-
-namespace BASE_HASH_NAMESPACE {
 
 // Implement hashing for pairs of at-most 32 bit integer values.
 // When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using
@@ -158,24 +128,61 @@ namespace BASE_HASH_NAMESPACE {
 //   h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32
 //
 // Contact danakj@chromium.org for any questions.
-#define DEFINE_32BIT_PAIR_HASH(type1, type2) \
-    DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
-      uint64 first = value.first; \
-      uint32 second = value.second; \
-      uint64 hash64 = (first << 32) | second; \
-      \
-      if (sizeof(std::size_t) >= sizeof(uint64)) \
-        return static_cast<std::size_t>(hash64); \
-      \
-      uint64 odd_random = 481046412LL << 32 | 1025306954LL; \
-      uint32 shift_random = 10121U << 16; \
-      \
-      hash64 = hash64 * odd_random + shift_random; \
-      std::size_t high_bits = static_cast<std::size_t>( \
-          hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
-      return high_bits; \
-    } \
-  DEFINE_PAIR_HASH_FUNCTION_END();
+inline std::size_t HashInts32(uint32 value1, uint32 value2) {
+  uint64 value1_64 = value1;
+  uint64 hash64 = (value1_64 << 32) | value2;
+
+  if (sizeof(std::size_t) >= sizeof(uint64))
+    return static_cast<std::size_t>(hash64);
+
+  uint64 odd_random = 481046412LL << 32 | 1025306955LL;
+  uint32 shift_random = 10121U << 16;
+
+  hash64 = hash64 * odd_random + shift_random;
+  std::size_t high_bits = static_cast<std::size_t>(
+      hash64 >> (sizeof(uint64) - sizeof(std::size_t)));
+  return high_bits;
+}
+
+// Implement hashing for pairs of up-to 64-bit integer values.
+// We use the compound integer hash method to produce a 64-bit hash code, by
+// breaking the two 64-bit inputs into 4 32-bit values:
+// http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
+// Then we reduce our result to 32 bits if required, similar to above.
+inline std::size_t HashInts64(uint64 value1, uint64 value2) {
+  uint32 short_random1 = 842304669U;
+  uint32 short_random2 = 619063811U;
+  uint32 short_random3 = 937041849U;
+  uint32 short_random4 = 3309708029U;
+
+  uint32 value1a = static_cast<uint32>(value1 & 0xffffffff);
+  uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff);
+  uint32 value2a = static_cast<uint32>(value2 & 0xffffffff);
+  uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff);
+
+  uint64 product1 = static_cast<uint64>(value1a) * short_random1;
+  uint64 product2 = static_cast<uint64>(value1b) * short_random2;
+  uint64 product3 = static_cast<uint64>(value2a) * short_random3;
+  uint64 product4 = static_cast<uint64>(value2b) * short_random4;
+
+  uint64 hash64 = product1 + product2 + product3 + product4;
+
+  if (sizeof(std::size_t) >= sizeof(uint64))
+    return static_cast<std::size_t>(hash64);
+
+  uint64 odd_random = 1578233944LL << 32 | 194370989LL;
+  uint32 shift_random = 20591U << 16;
+
+  hash64 = hash64 * odd_random + shift_random;
+  std::size_t high_bits = static_cast<std::size_t>(
+      hash64 >> (sizeof(uint64) - sizeof(std::size_t)));
+  return high_bits;
+}
+
+#define DEFINE_32BIT_PAIR_HASH(Type1, Type2) \
+inline std::size_t HashPair(Type1 value1, Type2 value2) { \
+  return HashInts32(value1, value2); \
+}
 
 DEFINE_32BIT_PAIR_HASH(int16, int16);
 DEFINE_32BIT_PAIR_HASH(int16, uint16);
@@ -196,44 +203,10 @@ DEFINE_32BIT_PAIR_HASH(uint32, uint32);
 
 #undef DEFINE_32BIT_PAIR_HASH
 
-// Implement hashing for pairs of up-to 64-bit integer values.
-// We use the compound integer hash method to produce a 64-bit hash code, by
-// breaking the two 64-bit inputs into 4 32-bit values:
-// http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
-// Then we reduce our result to 32 bits if required, similar to above.
-#define DEFINE_64BIT_PAIR_HASH(type1, type2) \
-    DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
-      uint32 short_random1 = 842304669U; \
-      uint32 short_random2 = 619063811U; \
-      uint32 short_random3 = 937041849U; \
-      uint32 short_random4 = 3309708029U; \
-      \
-      uint64 value1 = value.first; \
-      uint64 value2 = value.second; \
-      uint32 value1a = static_cast<uint32>(value1 & 0xffffffff); \
-      uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff); \
-      uint32 value2a = static_cast<uint32>(value2 & 0xffffffff); \
-      uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff); \
-      \
-      uint64 product1 = static_cast<uint64>(value1a) * short_random1; \
-      uint64 product2 = static_cast<uint64>(value1b) * short_random2; \
-      uint64 product3 = static_cast<uint64>(value2a) * short_random3; \
-      uint64 product4 = static_cast<uint64>(value2b) * short_random4; \
-      \
-      uint64 hash64 = product1 + product2 + product3 + product4; \
-      \
-      if (sizeof(std::size_t) >= sizeof(uint64)) \
-        return static_cast<std::size_t>(hash64); \
-      \
-      uint64 odd_random = 1578233944LL << 32 | 194370989LL; \
-      uint32 shift_random = 20591U << 16; \
-      \
-      hash64 = hash64 * odd_random + shift_random; \
-      std::size_t high_bits = static_cast<std::size_t>( \
-          hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
-      return high_bits; \
-    } \
-  DEFINE_PAIR_HASH_FUNCTION_END();
+#define DEFINE_64BIT_PAIR_HASH(Type1, Type2) \
+inline std::size_t HashPair(Type1 value1, Type2 value2) { \
+  return HashInts64(value1, value2); \
+}
 
 DEFINE_64BIT_PAIR_HASH(int16, int64);
 DEFINE_64BIT_PAIR_HASH(int16, uint64);
@@ -257,6 +230,32 @@ DEFINE_64BIT_PAIR_HASH(uint64, int64);
 DEFINE_64BIT_PAIR_HASH(uint64, uint64);
 
 #undef DEFINE_64BIT_PAIR_HASH
+}  // namespace base
+
+namespace BASE_HASH_NAMESPACE {
+
+// Implement methods for hashing a pair of integers, so they can be used as
+// keys in STL containers.
+
+#if defined(COMPILER_MSVC)
+
+template<typename Type1, typename Type2>
+inline std::size_t hash_value(const std::pair<Type1, Type2>& value) {
+  return base::HashPair(value.first, value.second);
+}
+
+#elif defined(COMPILER_GCC)
+template<typename Type1, typename Type2>
+struct hash<std::pair<Type1, Type2> > {
+  std::size_t operator()(std::pair<Type1, Type2> value) const {
+    return base::HashPair(value.first, value.second);
+  }
+};
+
+#else
+#error define hash<std::pair<Type1, Type2> > for your compiler
+#endif  // COMPILER
+
 }
 
 #undef DEFINE_PAIR_HASH_FUNCTION_START