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

#include "hash_fast.h"

#include <linux/compiler.h>

#ifndef fallthrough
#define fallthrough
#endif

static inline u64 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)

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

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

  return h;
}

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

static 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;
}

static inline uint64_t getblock64 ( const uint64_t * p, int i )
{
  uint64_t v;
  __builtin_memcpy(&v, &p[i], sizeof(uint64_t));
  return v;
}

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

uint64_t murmur_hash(const void * key, const int len)
{
  const uint8_t * data = (const uint8_t*)key;
  const int nblocks = len / 16;

  uint64_t h1 = 0;
  uint64_t h2 = 0;

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

  int i;

  const uint8_t * tail;
  uint64_t k1 = 0;
  uint64_t k2 = 0;

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

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

  for(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;
  }

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

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

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

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

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

  h1 ^= len; h2 ^= len;

  h1 += h2;
  h2 += h1;

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

  h1 += h2;
  h2 += h1;

  return h1;
}
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