The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/libkern/murmur3_32.c

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    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: stable/11/sys/libkern/murmur3_32.c 273268 2014-10-18 22:15:11Z des $
   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 

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