MURMUR3_FORCE_INLINE void MurmurHash3_x64_128()

in common/include/MurmurHash3.h [95:168]

• 53 lines of code
• 17 McCabe index (conditional complexity)

MURMUR3_FORCE_INLINE void MurmurHash3_x64_128(const void* key, size_t lenBytes,
                                              uint64_t seed, HashState& out) {
  static const uint64_t c1 = MURMUR3_BIG_CONSTANT(0x87c37b91114253d5);
  static const uint64_t c2 = MURMUR3_BIG_CONSTANT(0x4cf5ad432745937f);

  const uint8_t* data = (const uint8_t*)key;

  out.h1 = seed;
  out.h2 = seed;

  // Number of full 128-bit blocks of 16 bytes.
  // Possible exclusion of a remainder of up to 15 bytes.
  const size_t nblocks = lenBytes >> 4; // bytes / 16 

  // Process the 128-bit blocks (the body) into the hash
  const uint64_t* blocks = (const uint64_t*)(data);
  for (size_t i = 0; i < nblocks; ++i) { // 16 bytes per block
    uint64_t k1 = getblock64(blocks, i * 2 + 0);
    uint64_t k2 = getblock64(blocks, i * 2 + 1);

    k1 *= c1; k1  = MURMUR3_ROTL64(k1,31); k1 *= c2; out.h1 ^= k1;
    out.h1 = MURMUR3_ROTL64(out.h1,27);
    out.h1 += out.h2;
    out.h1 = out.h1*5+0x52dce729;

    k2 *= c2; k2  = MURMUR3_ROTL64(k2,33); k2 *= c1; out.h2 ^= k2;
    out.h2 = MURMUR3_ROTL64(out.h2,31);
    out.h2 += out.h1;
    out.h2 = out.h2*5+0x38495ab5;
  }

  // tail
  const uint8_t * tail = (const uint8_t*)(data + (nblocks << 4));

  uint64_t k1 = 0;
  uint64_t k2 = 0;

  switch(lenBytes & 15)
  {
  case 15: k2 ^= ((uint64_t)tail[14]) << 48; // falls through
  case 14: k2 ^= ((uint64_t)tail[13]) << 40; // falls through
  case 13: k2 ^= ((uint64_t)tail[12]) << 32; // falls through
  case 12: k2 ^= ((uint64_t)tail[11]) << 24; // falls through
  case 11: k2 ^= ((uint64_t)tail[10]) << 16; // falls through
  case 10: k2 ^= ((uint64_t)tail[ 9]) << 8;  // falls through
  case  9: k2 ^= ((uint64_t)tail[ 8]) << 0;
           k2 *= c2; k2  = MURMUR3_ROTL64(k2,33); k2 *= c1; out.h2 ^= k2;
           // falls through
  case  8: k1 ^= ((uint64_t)tail[ 7]) << 56; // falls through
  case  7: k1 ^= ((uint64_t)tail[ 6]) << 48; // falls through
  case  6: k1 ^= ((uint64_t)tail[ 5]) << 40; // falls through
  case  5: k1 ^= ((uint64_t)tail[ 4]) << 32; // falls through
  case  4: k1 ^= ((uint64_t)tail[ 3]) << 24; // falls through
  case  3: k1 ^= ((uint64_t)tail[ 2]) << 16; // falls through
  case  2: k1 ^= ((uint64_t)tail[ 1]) << 8; // falls through
  case  1: k1 ^= ((uint64_t)tail[ 0]) << 0;
           k1 *= c1; k1  = MURMUR3_ROTL64(k1,31); k1 *= c2; out.h1 ^= k1;
  };

  //----------
  // finalization

  out.h1 ^= lenBytes;
  out.h2 ^= lenBytes;

  out.h1 += out.h2;
  out.h2 += out.h1;

  out.h1 = fmix64(out.h1);
  out.h2 = fmix64(out.h2);

  out.h1 += out.h2;
  out.h2 += out.h1;
}