hash_mm3.cc

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/* SPDX-FileCopyrightText: 2018 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#include "BLI_compiler_attrs.h"
#include "BLI_compiler_compat.h"
#include "BLI_hash_mm3.hh" /* own include */
 
#if defined(_MSC_VER)
#  include <stdlib.h>
#  define ROTL32(x, y) _rotl(x, y)
#  define BIG_CONSTANT(x) (x)
 
/* Other compilers */
#else /* defined(_MSC_VER) */
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
 */
 
BLI_INLINE uint32_t getblock32(const uint32_t *p, int i)
{
  return p[i];
}
 
BLI_INLINE uint64_t getblock64(const uint64_t *p, int i)
{
  return p[i];
}
 
/* Finalization mix - force all bits of a hash block to avalanche */
 
BLI_INLINE uint32_t fmix32(uint32_t h)
{
  h ^= h >> 16;
  h *= 0x85ebca6b;
  h ^= h >> 13;
  h *= 0xc2b2ae35;
  h ^= h >> 16;
 
  return h;
}
 
BLI_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;
}
 
uint32_t BLI_hash_mm3(const uchar *data, size_t len, uint32_t seed)
{
  const uint8_t *in_data = (const uint8_t *)data;
  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 *)(in_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 *)(in_data + nblocks * 4);
 
  uint32_t k1 = 0;
 
  switch (len & 3) {
    case 3:
      k1 ^= tail[2] << 16;
      ATTR_FALLTHROUGH;
    case 2:
      k1 ^= tail[1] << 8;
      ATTR_FALLTHROUGH;
    case 1:
      k1 ^= tail[0];
      k1 *= c1;
      k1 = ROTL32(k1, 15);
      k1 *= c2;
      h1 ^= k1;
  }
 
  /* finalization */
 
  h1 ^= len;
 
  h1 = fmix32(h1);
 
  return h1;
}