src/v8/src/strings/string-hasher-inl.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_STRINGS_STRING_HASHER_INL_H_
#define V8_STRINGS_STRING_HASHER_INL_H_

#include "src/strings/string-hasher.h"

#include "src/objects/objects.h"
#include "src/objects/string-inl.h"
#include "src/strings/char-predicates-inl.h"
#include "src/utils/utils-inl.h"

namespace v8 {
namespace internal {

uint32_t StringHasher::AddCharacterCore(uint32_t running_hash, uint16_t c) {
  running_hash += c;
  running_hash += (running_hash << 10);
  running_hash ^= (running_hash >> 6);
  return running_hash;
}

uint32_t StringHasher::GetHashCore(uint32_t running_hash) {
  running_hash += (running_hash << 3);
  running_hash ^= (running_hash >> 11);
  running_hash += (running_hash << 15);
  int32_t hash = static_cast<int32_t>(running_hash & String::kHashBitMask);
  int32_t mask = (hash - 1) >> 31;
  return running_hash | (kZeroHash & mask);
}

uint32_t StringHasher::GetTrivialHash(int length) {
  DCHECK_GT(length, String::kMaxHashCalcLength);
  // String hash of a large string is simply the length.
  return (length << String::kHashShift) | String::kIsNotArrayIndexMask;
}

template <typename schar>
uint32_t StringHasher::HashSequentialString(const schar* chars, int length,
                                            uint64_t seed) {
  // Check whether the string is a valid array index. In that case, compute the
  // array index hash. It'll fall through to compute a regular string hash from
  // the start if it turns out that the string isn't a valid array index.
  if (IsInRange(length, 1, String::kMaxArrayIndexSize)) {
    if (IsDecimalDigit(chars[0]) && (length == 1 || chars[0] != '0')) {
      uint32_t index = chars[0] - '0';
      int i = 1;
      do {
        if (i == length) {
          return MakeArrayIndexHash(index, length);
        }
      } while (TryAddIndexChar(&index, chars[i++]));
    }
  } else if (length > String::kMaxHashCalcLength) {
    return GetTrivialHash(length);
  }

  // Non-array-index hash.
  DCHECK_LE(0, length);
  DCHECK_IMPLIES(0 < length, chars != nullptr);
  uint32_t running_hash = static_cast<uint32_t>(seed);
  const schar* end = &chars[length];
  while (chars != end) {
    running_hash = AddCharacterCore(running_hash, *chars++);
  }

  return (GetHashCore(running_hash) << String::kHashShift) |
         String::kIsNotArrayIndexMask;
}

std::size_t SeededStringHasher::operator()(const char* name) const {
  return StringHasher::HashSequentialString(
      name, static_cast<int>(strlen(name)), hashseed_);
}

}  // namespace internal
}  // namespace v8

#endif  // V8_STRINGS_STRING_HASHER_INL_H_