javascript 关联数组使用什么样的散列 function/algorithm？

Question

我们了解到有许多不同的哈希算法 algorithms/functions，我很好奇 javascript（v8，如果实施很重要）使用了哪一个。

Answer 1

既然V8是开源的，你去源码：

这是 GetHash()：https://github.com/v8/v8/blob/master/src/objects.cc#L903

而且，这里是一些不同类型的哈希函数：https://github.com/v8/v8-git-mirror/blob/bda7fb22465fc36d99b4053f0ef60cfaa8441209/src/utils.h#L347

而且，这看起来像是字符串的核心哈希计算：https://code.google.com/p/v8/source/browse/trunk/src/objects.cc?spec=svn6&r=6#3574

uint32_t String::ComputeHashCode(unibrow::CharacterStream* buffer,
                                 int length) {
  // Large string (please note large strings cannot be an array index).
  if (length > kMaxMediumStringSize) return HashField(length, false);

  // Note: the Jenkins one-at-a-time hash function
  uint32_t hash = 0;
  while (buffer->has_more()) {
    uc32 r = buffer->GetNext();
    hash += r;
    hash += (hash << 10);
    hash ^= (hash >> 6);
  }
  hash += (hash << 3);
  hash ^= (hash >> 11);
  hash += (hash << 15);

  // Short string.
  if (length <= kMaxShortStringSize) {
    // Make hash value consistent with value returned from String::Hash.
    buffer->Rewind();
    uint32_t index;
    hash = HashField(hash, ComputeArrayIndex(buffer, &index, length));
    hash = (hash & 0x00FFFFFF) | (length << kShortLengthShift);
    return hash;
  }

  // Medium string (please note medium strings cannot be an array index).
  ASSERT(length <= kMaxMediumStringSize);
  // Make hash value consistent with value returned from String::Hash.
  hash = HashField(hash, false);
  hash = (hash & 0x0000FFFF) | (length << kMediumLengthShift);
  return hash;
}

可能值得一提的是，V8 尽可能避免对对象属性使用散列 table，更愿意将已知的属性引用编译为直接索引引用而不是 [=26] =]-time hash lookups for performance reasons (though this is only possible sometimes - depends on the code).

javascript 关联数组使用什么样的散列 function/algorithm？

What kind of hashing function/algorithm does javascript associative array use?

javascript

associative-array

hashmap