murmur3_32.c

#include "murmur3_32.h"

// https://en.wikipedia.org/wiki/MurmurHash
static inline uint32_t murmur_32_scramble(uint32_t k)
{
    k *= 0xcc9e2d51;
    k = (k << 15) | (k >> 17);
    k *= 0x1b873593;
    return k;
}
uint32_t murmur3_32(const uint8_t* key, size_t len, uint32_t seed)
{
	uint32_t h = seed;
  uint32_t k;
  /* Read in groups of 4. */
  for (size_t i = len >> 2; i; i--) {
      // Here is a source of differing results across endiannesses.
      // A swap here has no effects on hash properties though.
      memcpy(&k, key, sizeof(uint32_t));
      key += sizeof(uint32_t);
      h ^= murmur_32_scramble(k);
      h = (h << 13) | (h >> 19);
      h = h * 5 + 0xe6546b64;
  }
  /* Read the rest. */
  k = 0;
  for (size_t i = len & 3; i; i--) {
      k <<= 8;
      k |= key[i - 1];
  }
  // A swap is *not* necessary here because the preceding loop already
  // places the low bytes in the low places according to whatever endianness
  // we use. Swaps only apply when the memory is copied in a chunk.
  h ^= murmur_32_scramble(k);
  /* Finalize. */
	h ^= len;
	h ^= h >> 16;
	h *= 0x85ebca6b;
	h ^= h >> 13;
	h *= 0xc2b2ae35;
	h ^= h >> 16;
	return h;
}