/*
 *
 * Copyright 2014, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include "src/core/support/murmur_hash.h"

#define ROTL32(x, r) ((x) << (r)) | ((x) >> (32 - (r)))

#define FMIX32(h)    \
  (h) ^= (h) >> 16;  \
  (h) *= 0x85ebca6b; \
  (h) ^= (h) >> 13;  \
  (h) *= 0xc2b2ae35; \
  (h) ^= (h) >> 16;

/* Block read - if your platform needs to do endian-swapping or can only
   handle aligned reads, do the conversion here */
#define GETBLOCK32(p, i) (p)[(i)]

gpr_uint32 gpr_murmur_hash3(const void* key, size_t len, gpr_uint32 seed) {
  const gpr_uint8* data = (const gpr_uint8*)key;
  const int nblocks = len / 4;
  int i;

  gpr_uint32 h1 = seed;
  gpr_uint32 k1 = 0;

  const gpr_uint32 c1 = 0xcc9e2d51;
  const gpr_uint32 c2 = 0x1b873593;

  const gpr_uint32* blocks = (const uint32_t*)(data + nblocks * 4);
  const uint8_t* tail = (const uint8_t*)(data + nblocks * 4);

  /* body */
  for (i = -nblocks; i; i++) {
    gpr_uint32 k1 = GETBLOCK32(blocks, i);

    k1 *= c1;
    k1 = ROTL32(k1, 15);
    k1 *= c2;

    h1 ^= k1;
    h1 = ROTL32(h1, 13);
    h1 = h1 * 5 + 0xe6546b64;
  }

  /* tail */
  switch (len & 3) {
    case 3:
      k1 ^= tail[2] << 16;
    case 2:
      k1 ^= tail[1] << 8;
    case 1:
      k1 ^= tail[0];
      k1 *= c1;
      k1 = ROTL32(k1, 15);
      k1 *= c2;
      h1 ^= k1;
  };

  /* finalization */
  h1 ^= len;
  FMIX32(h1);
  return h1;
}