MurmurHash3.h

#ifndef LSM_KV__MURMURHASH3_H_
#define LSM_KV__MURMURHASH3_H_

#if defined(_MSC_VER) && (_MSC_VER < 1600)

typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
typedef unsigned __int64 uint64_t;

#define FORCE_INLINE __forceinline

#include <stdlib.h>

#define ROTL64(x, y) _rotl64(x, y)

#define BIG_CONSTANT(x) (x)

// Other compilers

#else  // defined(_MSC_VER)

#include <stdint.h>

#define FORCE_INLINE inline __attribute__((always_inline))

inline uint64_t rotl64(uint64_t x, int8_t r) {
  return (x << r) | (x >> (64 - r));
}

#define ROTL64(x, y) rotl64(x, y)

#define BIG_CONSTANT(x) (x##LLU)

#endif  // !defined(_MSC_VER)

FORCE_INLINE uint64_t getblock64(const uint64_t *p, int i) { return p[i]; }

FORCE_INLINE uint64_t fmix64(uint64_t k) {
  k ^= k >> 33;
  k *= BIG_CONSTANT(0xff51afd7ed558ccd);
  k ^= k >> 33;
  k *= BIG_CONSTANT(0xc4ceb9fe1a85ec53);
  k ^= k >> 33;

  return k;
}

/**
* Murmur hash function
* @param key hash target.
* @param len byte number of key.
* @param seed use 1.
* @param out 128bit, use as 4 unsigned int.
* Example
  long long key = 103122;
  unsigned int hash[4] = {0};
  MurmurHash3_x64_128(&key, sizeof(key), 1, hash);
*/
static inline void MurmurHash3_x64_128(const void *key, const int len,
                                       const uint32_t seed, void *out) {
  const uint8_t *data = (const uint8_t *)key;
  const int nblocks = len / 16;

  uint64_t h1 = seed;
  uint64_t h2 = seed;

  const uint64_t c1 = BIG_CONSTANT(0x87c37b91114253d5);
  const uint64_t c2 = BIG_CONSTANT(0x4cf5ad432745937f);

  const uint64_t *blocks = (const uint64_t *)(data);

  for (int i = 0; i < nblocks; i++) {
    uint64_t k1 = getblock64(blocks, i * 2 + 0);
    uint64_t k2 = getblock64(blocks, i * 2 + 1);

    k1 *= c1;
    k1 = ROTL64(k1, 31);
    k1 *= c2;
    h1 ^= k1;

    h1 = ROTL64(h1, 27);
    h1 += h2;
    h1 = h1 * 5 + 0x52dce729;

    k2 *= c2;
    k2 = ROTL64(k2, 33);
    k2 *= c1;
    h2 ^= k2;

    h2 = ROTL64(h2, 31);
    h2 += h1;
    h2 = h2 * 5 + 0x38495ab5;
  }

  const uint8_t *tail = (const uint8_t *)(data + nblocks * 16);

  uint64_t k1 = 0;
  uint64_t k2 = 0;

  switch (len & 15) {
    case 15:
      k2 ^= ((uint64_t)tail[14]) << 48;
    case 14:
      k2 ^= ((uint64_t)tail[13]) << 40;
    case 13:
      k2 ^= ((uint64_t)tail[12]) << 32;
    case 12:
      k2 ^= ((uint64_t)tail[11]) << 24;
    case 11:
      k2 ^= ((uint64_t)tail[10]) << 16;
    case 10:
      k2 ^= ((uint64_t)tail[9]) << 8;
    case 9:
      k2 ^= ((uint64_t)tail[8]) << 0;
      k2 *= c2;
      k2 = ROTL64(k2, 33);
      k2 *= c1;
      h2 ^= k2;

    case 8:
      k1 ^= ((uint64_t)tail[7]) << 56;
    case 7:
      k1 ^= ((uint64_t)tail[6]) << 48;
    case 6:
      k1 ^= ((uint64_t)tail[5]) << 40;
    case 5:
      k1 ^= ((uint64_t)tail[4]) << 32;
    case 4:
      k1 ^= ((uint64_t)tail[3]) << 24;
    case 3:
      k1 ^= ((uint64_t)tail[2]) << 16;
    case 2:
      k1 ^= ((uint64_t)tail[1]) << 8;
    case 1:
      k1 ^= ((uint64_t)tail[0]) << 0;
      k1 *= c1;
      k1 = ROTL64(k1, 31);
      k1 *= c2;
      h1 ^= k1;
  };

  h1 ^= len;
  h2 ^= len;

  h1 += h2;
  h2 += h1;

  h1 = fmix64(h1);
  h2 = fmix64(h2);

  h1 += h2;
  h2 += h1;

  ((uint64_t *)out)[0] = h1;
  ((uint64_t *)out)[1] = h2;
}

#endif  // LSM_KV__MURMURHASH3_H_