MurmurHash3Inl.h

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#pragma once

#include "../Shared/funcannotations.h"

FORCE_INLINE DEVICE uint32_t rotl32(uint32_t x, int8_t r) {
  return (x << r) | (x >> (32 - r));
}

#define ROTL32(x, y) rotl32(x, y)

FORCE_INLINE DEVICE uint32_t MurmurHash3Impl(const void* key, int len, uint32_t seed) {
  const uint8_t* data = (const uint8_t*)key;
  const int nblocks = len / 4;

  uint32_t h1 = seed;

  const uint32_t c1 = 0xcc9e2d51;
  const uint32_t c2 = 0x1b873593;

  //----------
  // body

  const uint32_t* blocks = (const uint32_t*)(data + nblocks * 4);

  for (int i = -nblocks; i; i++) {
    uint32_t k1 = blocks[i];

    k1 *= c1;
    k1 = ROTL32(k1, 15);
    k1 *= c2;

    h1 ^= k1;
    h1 = ROTL32(h1, 13);
    h1 = h1 * 5 + 0xe6546b64;
  }

  //----------
  // tail

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

  uint32_t k1 = 0;

  switch (len & 3) {
    case 3:
      k1 ^= tail[2] << 16;
    case 2:
      k1 ^= tail[1] << 8;
    case 1:
      k1 ^= tail[0];
      k1 *= c1;
      k1 = ROTL32(k1, 15);
      k1 *= c2;
      h1 ^= k1;
  };

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

  h1 ^= len;

  //-----------------------------------------------------------------------------
  // Finalization mix - force all bits of a hash block to avalanche

  h1 ^= h1 >> 16;
  h1 *= 0x85ebca6b;
  h1 ^= h1 >> 13;
  h1 *= 0xc2b2ae35;
  h1 ^= h1 >> 16;

  return h1;
}