base/hash/hash.h

// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_HASH_HASH_H_
#define BASE_HASH_HASH_H_

#include <stddef.h>
#include <stdint.h>

#include <limits>
#include <string>
#include <utility>

#include "base/base_export.h"
#include "base/containers/span.h"
#include "base/strings/string_piece.h"

namespace base {

// WARNING: This hash functions should not be used for any cryptographic
// purpose.

// Deprecated: Computes a hash of a memory buffer, use FastHash() instead.
// If you need to persist a change on disk or between computers, use
// PersistentHash().
// TODO(https://crbug.com/1025358): Migrate client code to new hash function.
BASE_EXPORT uint32_t Hash(const void* data, size_t length);
BASE_EXPORT uint32_t Hash(const std::string& str);
BASE_EXPORT uint32_t Hash(const std::u16string& str);

// Really *fast* and high quality hash.
// Recommended hash function for general use, we pick the best performant
// hash for each build target.
// It is prone to be updated whenever a newer/faster hash function is
// publicly available.
// May changed without warning, do not expect stability of outputs.
BASE_EXPORT size_t FastHash(base::span<const uint8_t> data);
inline size_t FastHash(StringPiece str) {
  return FastHash(as_bytes(make_span(str)));
}

// Computes a hash of a memory buffer. This hash function must not change so
// that code can use the hashed values for persistent storage purposes or
// sending across the network. If a new persistent hash function is desired, a
// new version will have to be added in addition.
//
// WARNING: This hash function should not be used for any cryptographic purpose.
BASE_EXPORT uint32_t PersistentHash(base::span<const uint8_t> data);
BASE_EXPORT uint32_t PersistentHash(const void* data, size_t length);
BASE_EXPORT uint32_t PersistentHash(const std::string& str);

// Hash pairs of 32-bit or 64-bit numbers.
BASE_EXPORT size_t HashInts32(uint32_t value1, uint32_t value2);
BASE_EXPORT size_t HashInts64(uint64_t value1, uint64_t value2);

template <typename T1, typename T2>
inline size_t HashInts(T1 value1, T2 value2) {
  // This condition is expected to be compile-time evaluated and optimised away
  // in release builds.
  if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t)))
    return HashInts64(value1, value2);

  return HashInts32(static_cast<uint32_t>(value1),
                    static_cast<uint32_t>(value2));
}

// A templated hasher for pairs of integer types. Example:
//
//   using MyPair = std::pair<int32_t, int32_t>;
//   std::unordered_set<MyPair, base::IntPairHash<MyPair>> set;
template <typename T>
struct IntPairHash;

template <typename Type1, typename Type2>
struct IntPairHash<std::pair<Type1, Type2>> {
  size_t operator()(std::pair<Type1, Type2> value) const {
    return HashInts(value.first, value.second);
  }
};

}  // namespace base

#endif  // BASE_HASH_HASH_H_