murmur3_hash.c

//-----------------------------------------------------------------------------
// MurmurHash3 was written by Austin Appleby, and is placed in the public
// domain. The author hereby disclaims copyright to this source code.

// Note - The x86 and x64 versions do _not_ produce the same results, as the
// algorithms are optimized for their respective platforms. You can still
// compile and run any of them on any platform, but your performance with the
// non-native version will be less than optimal.

#include "murmur3_hash.h"

//-----------------------------------------------------------------------------
// Platform-specific functions and macros

// Microsoft Visual Studio

#if defined(_MSC_VER)

#define FORCE_INLINE    __forceinline

#include <stdlib.h>

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

#define BIG_CONSTANT(x) (x)

// Other compilers

#else    // defined(_MSC_VER)

#define    FORCE_INLINE inline __attribute__((always_inline))

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

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

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

#endif // !defined(_MSC_VER)

//-----------------------------------------------------------------------------
// Block read - if your platform needs to do endian-swapping or can only
// handle aligned reads, do the conversion here

static FORCE_INLINE uint32_t getblock32 ( const uint32_t * p, int i )
{
  return p[i];
}

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

static FORCE_INLINE uint32_t fmix32 ( uint32_t h )
{
  h ^= h >> 16;
  h *= 0x85ebca6b;
  h ^= h >> 13;
  h *= 0xc2b2ae35;
  h ^= h >> 16;

  return h;
}

//-----------------------------------------------------------------------------

/* Definition modified slightly from the public domain interface (no seed +
 * return value */
uint32_t MurmurHash3_x86_32 ( const void * key, size_t length)
{
  const uint8_t * data = (const uint8_t*)key;
  const int nblocks = length / 4;

  uint32_t h1 = 0;

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

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

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

  for(int i = -nblocks; i; i++)
  {
    uint32_t k1 = getblock32(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(length & 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 ^= length;

  h1 = fmix32(h1);

  //*(uint32_t*)out = h1;
  return h1;
}