neatvnc/src/murmurhash.c

/*
 * The MIT License (MIT)
 * 
 * Copyright (c) 2014 Joseph Werle
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include "murmurhash.h"

uint32_t
murmurhash (const char *key, uint32_t len, uint32_t seed) {
  uint32_t c1 = 0xcc9e2d51;
  uint32_t c2 = 0x1b873593;
  uint32_t r1 = 15;
  uint32_t r2 = 13;
  uint32_t m = 5;
  uint32_t n = 0xe6546b64;
  uint32_t h = 0;
  uint32_t k = 0;
  uint8_t *d = (uint8_t *) key; // 32 bit extract from `key'
  const uint32_t *chunks = NULL;
  const uint8_t *tail = NULL; // tail - last 8 bytes
  int i = 0;
  int l = len / 4; // chunk length

  h = seed;

  chunks = (const uint32_t *) (d + l * 4); // body
  tail = (const uint8_t *) (d + l * 4); // last 8 byte chunk of `key'

  // for each 4 byte chunk of `key'
  for (i = -l; i != 0; ++i) {
    // next 4 byte chunk of `key'
    k = chunks[i];

    // encode next 4 byte chunk of `key'
    k *= c1;
    k = (k << r1) | (k >> (32 - r1));
    k *= c2;

    // append to hash
    h ^= k;
    h = (h << r2) | (h >> (32 - r2));
    h = h * m + n;
  }

  k = 0;

  // remainder
  switch (len & 3) { // `len % 4'
    case 3: k ^= (tail[2] << 16);
      // fallthrough
    case 2: k ^= (tail[1] << 8);
      // fallthrough
    case 1:
      k ^= tail[0];
      k *= c1;
      k = (k << r1) | (k >> (32 - r1));
      k *= c2;
      h ^= k;
  }

  h ^= len;

  h ^= (h >> 16);
  h *= 0x85ebca6b;
  h ^= (h >> 13);
  h *= 0xc2b2ae35;
  h ^= (h >> 16);

  return h;
}