sys/libkern/murmur3_32.c

   1 /*-
   2  * Copyright (c) 2014 Dag-Erling Smørgrav
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * $FreeBSD$
  27  */
  28
  29 #include <sys/hash.h>
  30 #include <sys/endian.h>
  31 #include <sys/stdint.h>
  32 #include <sys/types.h>
  33
  34 #define rol32(i32, n) ((i32) << (n) | (i32) >> (32 - (n)))
  35
  36 /*
  37  * Simple implementation of the Murmur3-32 hash function.
  38  *
  39  * This implementation is slow but safe.  It can be made significantly
  40  * faster if the caller guarantees that the input is correctly aligned for
  41  * 32-bit reads, and slightly faster yet if the caller guarantees that the
  42  * length of the input is always a multiple of 4 bytes.
  43  */
  44 uint32_t
  45 murmur3_32_hash(const void *data, size_t len, uint32_t seed)
  46 {
  47         const uint8_t *bytes;
  48         uint32_t hash, k;
  49         size_t res;
  50
  51         /* initialization */
  52         bytes = data;
  53         res = len;
  54         hash = seed;
  55
  56         /* main loop */
  57         while (res >= 4) {
  58                 /* replace with le32toh() if input is aligned */
  59                 k = le32dec(bytes);
  60                 bytes += 4;
  61                 res -= 4;
  62                 k *= 0xcc9e2d51;
  63                 k = rol32(k, 15);
  64                 k *= 0x1b873593;
  65                 hash ^= k;
  66                 hash = rol32(hash, 13);
  67                 hash *= 5;
  68                 hash += 0xe6546b64;
  69         }
  70
  71         /* remainder */
  72         /* remove if input length is a multiple of 4 */
  73         if (res > 0) {
  74                 k = 0;
  75                 switch (res) {
  76                 case 3:
  77                         k |= bytes[2] << 16;
  78                 case 2:
  79                         k |= bytes[1] << 8;
  80                 case 1:
  81                         k |= bytes[0];
  82                         k *= 0xcc9e2d51;
  83                         k = rol32(k, 15);
  84                         k *= 0x1b873593;
  85                         hash ^= k;
  86                         break;
  87                 }
  88         }
  89
  90         /* finalize */
  91         hash ^= (uint32_t)len;
  92         hash ^= hash >> 16;
  93         hash *= 0x85ebca6b;
  94         hash ^= hash >> 13;
  95         hash *= 0xc2b2ae35;
  96         hash ^= hash >> 16;
  97         return (hash);
  98 }
  99
 100 /*
 101  * Simplified version of the above optimized for aligned sequences of
 102  * 32-bit words.  The count argument is the number of words, not the
 103  * length in bytes.
 104  */
 105 uint32_t
 106 murmur3_32_hash32(const uint32_t *data, size_t count, uint32_t seed)
 107 {
 108         uint32_t hash, k;
 109         size_t res;
 110
 111         /* iterate */
 112         for (res = count, hash = seed; res > 0; res--, data++) {
 113                 k = le32toh(*data);
 114                 k *= 0xcc9e2d51;
 115                 k = rol32(k, 15);
 116                 k *= 0x1b873593;
 117                 hash ^= k;
 118                 hash = rol32(hash, 13);
 119                 hash *= 5;
 120                 hash += 0xe6546b64;
 121         }
 122
 123         /* finalize */
 124         hash ^= (uint32_t)count;
 125         hash ^= hash >> 16;
 126         hash *= 0x85ebca6b;
 127         hash ^= hash >> 13;
 128         hash *= 0xc2b2ae35;
 129         hash ^= hash >> 16;
 130         return (hash);
 131 }
 132