ESP32-PaxCounter/src/hash.cpp

/*
 * RokkitHash - Arduino port for Paul Hsieh's "SuperFastHash"
 *
 * A very quick hash function, (c) Paul Hsieh
 *
 * See http://www.azillionmonkeys.com/qed/hash.html for more information
 * about its inner workings
 *
 * - Initial Arduino version: 2014 Alex K
 * - 8-bit improvements: robtillaart
 * - Current maintainer: SukkoPera <software@sukkology.net>
 *
 * See http://forum.arduino.cc/index.php?topic=226686.0 for some talk
 * about the various improvements.
 *
 * 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 "hash.h"

uint32_t IRAM_ATTR rokkit(const char *data, int len) {
  uint32_t hash, tmp;
  int rem;

  if (len <= 0 || data == 0)
    return 0;
  hash = len;
  rem = len & 3;
  len >>= 2;

  /* Main loop */
  while (len > 0) {
    hash += *((uint16_t *)data);
    tmp = (*((uint16_t *)(data + 2)) << 11) ^ hash;
    hash = (hash << 16) ^ tmp;
    data += 2 * 2;
    hash += hash >> 11;
    len--;
  }

  /* Handle end cases */
  switch (rem) {
  case 3:
    hash += *((uint16_t *)data);
    hash ^= hash << 16;
    hash ^= ((signed char)data[2]) << 18;
    hash += hash >> 11;
    break;
  case 2:
    hash += *((uint16_t *)data);
    hash ^= hash << 11;
    hash += hash >> 17;
    break;
  case 1:
    hash += (signed char)*data;
    hash ^= hash << 10;
    hash += hash >> 1;
  }

  /* Force "avalanching" of final 127 bits */
  hash ^= hash << 3;
  hash += hash >> 5;
  hash ^= hash << 4;
  hash += hash >> 17;
  hash ^= hash << 25;
  hash += hash >> 6;

  return hash;
}