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

src/base/functional.h

+// 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.
+
+#ifndef V8_BASE_FUNCTIONAL_H_
+#define V8_BASE_FUNCTIONAL_H_
+
+#include <cstddef>
+#include <functional>
+#include <utility>
+
+#include "include/v8stdint.h"
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace base {
+
+// base::hash is an implementation of the hash function object specified by
+// C++11. It was designed to be compatible with std::hash (in C++11) and
+// boost:hash (which in turn is based on the hash function object specified by
+// the Draft Technical Report on C++ Library Extensions (TR1)).
+//
+// base::hash is implemented by calling the hash_value function. The namespace
+// isn't specified so that it can detect overloads via argument dependant
+// lookup. So if there is a free function hash_value in the same namespace as a
+// custom type, it will get called.
+//
+// If users are asked to implement a hash function for their own types with no
+// guidance, they generally write bad hash functions. Instead, we provide  a
+// simple function base::hash_combine to pass hash-relevant member variables
+// into, in order to define a decent hash function. base::hash_combine is
+// declared as:
+//
+//   template<typename T, typename... Ts>
+//   size_t hash_combine(const T& v, const Ts& ...vs);
+//
+// Consider the following example:
+//
+//   namespace v8 {
+//   namespace bar {
+//     struct Point { int x; int y; };
+//     size_t hash_value(Point const& p) {
+//       return base::hash_combine(p.x, p.y);
+//     }
+//   }
+//
+//   namespace foo {
+//     void DoSomeWork(bar::Point const& p) {
+//       base::hash<bar::Point> h;
+//       ...
+//       size_t hash_code = h(p);  // calls bar::hash_value(Point const&)
+//       ...
+//     }
+//   }
+//   }
+//
+// Based on the "Hashing User-Defined Types in C++1y" proposal from Jeffrey
+// Yasskin and Chandler Carruth, see
+// http://www.open-std.org/Jtc1/sc22/wg21/docs/papers/2012/n3333.html.
+
+template <typename>
+struct hash;
+
+
+inline size_t hash_combine() { return 0u; }
+inline size_t hash_combine(size_t seed) { return seed; }
+size_t hash_combine(size_t seed, size_t value);
+template <typename T, typename... Ts>
+inline size_t hash_combine(T const& v, Ts const&... vs) {
+  return hash_combine(hash<T>()(v), hash_combine(vs...));
+}
+
+
+#define V8_BASE_HASH_VALUE_TRIVIAL(type) \
+  inline size_t hash_value(type v) { return static_cast<size_t>(v); }
+V8_BASE_HASH_VALUE_TRIVIAL(bool)
+V8_BASE_HASH_VALUE_TRIVIAL(unsigned char)
+V8_BASE_HASH_VALUE_TRIVIAL(unsigned short)  // NOLINT(runtime/int)
+V8_BASE_HASH_VALUE_TRIVIAL(unsigned int)
+#undef V8_BASE_HASH_VALUE_TRIVIAL
+
+size_t hash_value(unsigned long v);       // NOLINT(runtime/int)
+size_t hash_value(unsigned long long v);  // NOLINT(runtime/int)
+
+#define V8_BASE_HASH_VALUE_SIGNED(type)            \
+  inline size_t hash_value(signed type v) {        \
+    return hash_value(bit_cast<unsigned type>(v)); \
+  }
+V8_BASE_HASH_VALUE_SIGNED(char)
+V8_BASE_HASH_VALUE_SIGNED(short)      // NOLINT(runtime/int)
+V8_BASE_HASH_VALUE_SIGNED(int)        // NOLINT(runtime/int)
+V8_BASE_HASH_VALUE_SIGNED(long)       // NOLINT(runtime/int)
+V8_BASE_HASH_VALUE_SIGNED(long long)  // NOLINT(runtime/int)
+#undef V8_BASE_HASH_VALUE_SIGNED
+
+size_t hash_value(float v);
+size_t hash_value(double v);
+
+template <typename T>
+inline size_t hash_value(T* const& v) {
+  size_t const x = bit_cast<size_t>(v);
+  return (x >> 3) + x;
+}
+
+template <typename T1, typename T2>
+inline size_t hash_value(std::pair<T1, T2> const& v) {
+  return hash_combine(v.first, v.second);
+}
+
+
+template <typename T>
+struct hash : public std::unary_function<T, size_t> {
+  size_t operator()(T const& v) const { return hash_value(v); }
+};
+
+#define V8_BASE_HASH_SPECIALIZE(type)                            \
+  template <>                                                    \
+  struct hash<type> : public std::unary_function<type, size_t> { \
+    size_t operator()(type const v) const {                      \
+      return ::v8::base::hash_value(v);                          \
+    }                                                            \
+  };
+V8_BASE_HASH_SPECIALIZE(bool)
+V8_BASE_HASH_SPECIALIZE(signed char)
+V8_BASE_HASH_SPECIALIZE(unsigned char)
+V8_BASE_HASH_SPECIALIZE(short)           // NOLINT(runtime/int)
+V8_BASE_HASH_SPECIALIZE(unsigned short)  // NOLINT(runtime/int)
+V8_BASE_HASH_SPECIALIZE(int)
+V8_BASE_HASH_SPECIALIZE(unsigned int)
+V8_BASE_HASH_SPECIALIZE(long)                // NOLINT(runtime/int)
+V8_BASE_HASH_SPECIALIZE(unsigned long)       // NOLINT(runtime/int)
+V8_BASE_HASH_SPECIALIZE(long long)           // NOLINT(runtime/int)
+V8_BASE_HASH_SPECIALIZE(unsigned long long)  // NOLINT(runtime/int)
+V8_BASE_HASH_SPECIALIZE(float)
+V8_BASE_HASH_SPECIALIZE(double)
+#undef V8_BASE_HASH_SPECIALIZE
+
+template <typename T>
+struct hash<T*> : public std::unary_function<T*, size_t> {
+  size_t operator()(T* const v) const { return ::v8::base::hash_value(v); }
+};
+
+template <typename T1, typename T2>
+struct hash<std::pair<T1, T2> >
+    : public std::unary_function<std::pair<T1, T2>, size_t> {
+  size_t operator()(std::pair<T1, T2> const& v) const {
+    return ::v8::base::hash_value(v);
+  }
+};
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_FUNCTIONAL_H_