Add C++11 compatible base::hash function object.

src/base/functional.cc

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// This also contains public domain code from MurmurHash. From the
+// MurmurHash header:
+//
+// MurmurHash3 was written by Austin Appleby, and is placed in the public
+// domain. The author hereby disclaims copyright to this source code.
+
+#include "src/base/functional.h"
+
+#include <limits>
+
+#include "src/base/bits.h"
+
+namespace v8 {
+namespace base {
+
+namespace {
+
+template <typename T>
+inline size_t hash_value_unsigned(T value) {
+  const unsigned size_t_bits = std::numeric_limits<size_t>::digits;
+  // ceiling(std::numeric_limits<T>::digits / size_t_bits) - 1
+  const unsigned length = (std::numeric_limits<T>::digits - 1) / size_t_bits;
+  size_t seed = 0;
+  // Hopefully, this loop can be unrolled.
+  for (unsigned i = length * size_t_bits; i > 0; i -= size_t_bits) {
+    seed ^= static_cast<size_t>(value >> i) + (seed << 6) + (seed >> 2);
+  }
+  seed ^= static_cast<size_t>(value) + (seed << 6) + (seed >> 2);
+  return seed;
+}
+
+}  // namespace
+
+
+// This code was taken from MurmurHash.
+size_t hash_combine(size_t seed, size_t value) {
+#if V8_HOST_ARCH_32_BIT
+  const uint32_t c1 = 0xcc9e2d51;
+  const uint32_t c2 = 0x1b873593;
+
+  value *= c1;
+  value = bits::RotateRight32(value, 15);
+  value *= c2;
+
+  seed ^= value;
+  seed = bits::RotateRight32(seed, 13);
+  seed = seed * 5 + 0xe6546b64;
+#else
+  const uint64_t m = V8_UINT64_C(0xc6a4a7935bd1e995);
+  const uint32_t r = 47;
+
+  value *= m;
+  value ^= value >> r;
+  value *= m;
+
+  seed ^= value;
+  seed *= m;
+#endif  // V8_HOST_ARCH_32_BIT
+  return seed;
+}
+
+
+size_t hash_value(unsigned long v) {  // NOLINT(runtime/int)
+  return hash_value_unsigned(v);
+}
+
+
+size_t hash_value(unsigned long long v) {  // NOLINT(runtime/int)
+  return hash_value_unsigned(v);
+}
+
+
+size_t hash_value(float v) {
+  // 0 and -0 both hash to zero.
+  return v != 0.0f ? hash_value(bit_cast<uint32_t>(v)) : 0;
+}
+
+
+size_t hash_value(double v) {
+  // 0 and -0 both hash to zero.
+  return v != 0.0 ? hash_value(bit_cast<uint64_t>(v)) : 0;
+}
+
+}  // namespace base
+}  // namespace v8