src/runtime/murmur_hash.c

   1 /*
   2  *
   3  * Copyright 2015, Google Inc.
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions are
   8  * met:
   9  *
  10  *     * Redistributions of source code must retain the above copyright
  11  * notice, this list of conditions and the following disclaimer.
  12  *     * Redistributions in binary form must reproduce the above
  13  * copyright notice, this list of conditions and the following disclaimer
  14  * in the documentation and/or other materials provided with the
  15  * distribution.
  16  *     * Neither the name of Google Inc. nor the names of its
  17  * contributors may be used to endorse or promote products derived from
  18  * this software without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  21  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  23  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  24  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  25  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  26  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  27  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  28  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  29  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  30  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  31  *
  32  */
  33
  34 #include "murmur_hash.h"
  35
  36 #define ROTL32(x, r) ((x) << (r)) | ((x) >> (32 - (r)))
  37
  38 #define FMIX32(h)    \
  39   (h) ^= (h) >> 16;  \
  40   (h) *= 0x85ebca6b; \
  41   (h) ^= (h) >> 13;  \
  42   (h) *= 0xc2b2ae35; \
  43   (h) ^= (h) >> 16;
  44
  45 /* Block read - if your platform needs to do endian-swapping or can only
  46    handle aligned reads, do the conversion here */
  47 #define GETBLOCK32(p, i) (p)[(i)]
  48
  49 uint32_t gpr_murmur_hash3(const void *key, size_t len, uint32_t seed) {
  50   const uint8_t *data = (const uint8_t *)key;
  51   const size_t nblocks = len / 4;
  52   int i;
  53
  54   uint32_t h1 = seed;
  55   uint32_t k1;
  56
  57   const uint32_t c1 = 0xcc9e2d51;
  58   const uint32_t c2 = 0x1b873593;
  59
  60   const uint32_t *blocks = ((const uint32_t *)key) + nblocks;
  61   const uint8_t *tail = (const uint8_t *)(data + nblocks * 4);
  62
  63   /* body */
  64   for (i = -(int)nblocks; i; i++) {
  65     k1 = GETBLOCK32(blocks, i);
  66
  67     k1 *= c1;
  68     k1 = ROTL32(k1, 15);
  69     k1 *= c2;
  70
  71     h1 ^= k1;
  72     h1 = ROTL32(h1, 13);
  73     h1 = h1 * 5 + 0xe6546b64;
  74   }
  75
  76   k1 = 0;
  77
  78   /* tail */
  79   switch (len & 3) {
  80     case 3:
  81       k1 ^= ((uint32_t)tail[2]) << 16;
  82     case 2:
  83       k1 ^= ((uint32_t)tail[1]) << 8;
  84     case 1:
  85       k1 ^= tail[0];
  86       k1 *= c1;
  87       k1 = ROTL32(k1, 15);
  88       k1 *= c2;
  89       h1 ^= k1;
  90   };
  91
  92   /* finalization */
  93   h1 ^= (uint32_t)len;
  94   FMIX32(h1);
  95   return h1;
  96 }