Function _Hash_bytes

src/Common/StringUtils/StringUtils.cpp:131–174

Implementation of Murmur hash for 32-bit size_t.

  // Implementation of Murmur hash for 32-bit size_t.
  size_t
  _Hash_bytes(const void* ptr, size_t len, size_t seed)
  {
    const size_t m = 0x5bd1e995;
    size_t hash = seed ^ len;
    const char* buf = static_cast<const char*>(ptr);

    // Mix 4 bytes at a time into the hash.
    while(len >= 4)
      {
	size_t k = unaligned_load(buf);
	k *= m;
	k ^= k >> 24;
	k *= m;
	hash *= m;
	hash ^= k;
	buf += 4;
	len -= 4;
      }

    size_t k;
    // Handle the last few bytes of the input array.
    switch(len)
      {
      case 3:
	k = static_cast<unsigned char>(buf[2]);
	hash ^= k << 16;
	[[gnu::fallthrough]];
      case 2:
	k = static_cast<unsigned char>(buf[1]);
	hash ^= k << 8;
	[[gnu::fallthrough]];
      case 1:
	k = static_cast<unsigned char>(buf[0]);
	hash ^= k;
	hash *= m;
      };

    // Do a few final mixes of the hash.
    hash ^= hash >> 13;
    hash *= m;
    hash ^= hash >> 15;
    return hash;
  }

#elif __SIZEOF_SIZE_T__ == 8