v8/src/string-hasher.h

// Copyright 2017 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_STRING_HASHER_H_
#define V8_STRING_HASHER_H_

#include "src/globals.h"

namespace v8 {
namespace internal {

template <typename T>
class Vector;

class V8_EXPORT_PRIVATE StringHasher final {
 public:
  StringHasher() = delete;
  template <typename schar>
  static inline uint32_t HashSequentialString(const schar* chars, int length,
                                              uint64_t seed);

  // Calculated hash value for a string consisting of 1 to
  // String::kMaxArrayIndexSize digits with no leading zeros (except "0").
  // value is represented decimal value.
  static uint32_t MakeArrayIndexHash(uint32_t value, int length);

  // No string is allowed to have a hash of zero.  That value is reserved
  // for internal properties.  If the hash calculation yields zero then we
  // use 27 instead.
  static const int kZeroHash = 27;

  // Reusable parts of the hashing algorithm.
  V8_INLINE static uint32_t AddCharacterCore(uint32_t running_hash, uint16_t c);
  V8_INLINE static uint32_t GetHashCore(uint32_t running_hash);

  static inline uint32_t GetTrivialHash(int length);
};

// Useful for std containers that require something ()'able.
struct SeededStringHasher {
  explicit SeededStringHasher(uint64_t hashseed) : hashseed_(hashseed) {}
  inline std::size_t operator()(const char* name) const;

  uint64_t hashseed_;
};

// Useful for std containers that require something ()'able.
struct StringEquals {
  bool operator()(const char* name1, const char* name2) const {
    return strcmp(name1, name2) == 0;
  }
};

}  // namespace internal
}  // namespace v8

#endif  // V8_STRING_HASHER_H_