uspace/lib/c/include/adt/hash.h

   1 /*
   2  * Copyright (c) 2012 Adam Hraska
   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  *
   9  * - Redistributions of source code must retain the above copyright
  10  *   notice, this list of conditions and the following disclaimer.
  11  * - Redistributions in binary form must reproduce the above copyright
  12  *   notice, this list of conditions and the following disclaimer in the
  13  *   documentation and/or other materials provided with the distribution.
  14  * - The name of the author may not be used to endorse or promote products
  15  *   derived from this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 /** @addtogroup genericadt
  30  * @{
  31  */
  32 /** @file
  33  */
  34 #ifndef KERN_HASH_H_
  35 #define KERN_HASH_H_
  36
  37 #include <stdint.h>
  38 #include <libarch/types.h>
  39
  40 /** Produces a uniform hash affecting all output bits from the skewed input. */
  41 static inline uint32_t hash_mix32(uint32_t hash)
  42 {
  43         /*
  44          * Thomas Wang's modification of Bob Jenkin's hash mixing function:
  45          * http://www.concentric.net/~Ttwang/tech/inthash.htm
  46          * Public domain.
  47          */
  48         hash = ~hash + (hash << 15);
  49         hash = hash ^ (hash >> 12);
  50         hash = hash + (hash << 2);
  51         hash = hash ^ (hash >> 4);
  52         hash = hash * 2057;
  53         hash = hash ^ (hash >> 16);
  54         return hash;
  55 }
  56
  57 /** Produces a uniform hash affecting all output bits from the skewed input. */
  58 static inline uint64_t hash_mix64(uint64_t hash)
  59 {
  60         /*
  61          * Thomas Wang's public domain 64-bit hash mixing function:
  62          * http://www.concentric.net/~Ttwang/tech/inthash.htm
  63          */
  64         hash = (hash ^ 61) ^ (hash >> 16);
  65         hash = hash + (hash << 3);
  66         hash = hash ^ (hash >> 4);
  67         hash = hash * 0x27d4eb2d;
  68         hash = hash ^ (hash >> 15);
  69         /*
  70          * Lower order bits are mixed more thoroughly. Swap them with
  71          * the higher order bits and make the resulting higher order bits
  72          * more usable.
  73          */
  74         return (hash << 32) | (hash >> 32);
  75 }
  76
  77 /** Produces a uniform hash affecting all output bits from the skewed input. */
  78 static inline size_t hash_mix(size_t hash)
  79 {
  80 #ifdef __32_BITS__
  81         return hash_mix32(hash);
  82 #elif defined(__64_BITS__)
  83         return hash_mix64(hash);
  84 #else
  85 #error Unknown size_t size - cannot select proper hash mix function.
  86 #endif
  87 }
  88
  89 /** Use to create a hash from multiple values.
  90  *
  91  * Typical usage:
  92  * @code
  93  * int car_id;
  94  * bool car_convertible;
  95  * // ..
  96  * size_t hash = 0;
  97  * hash = hash_combine(hash, car_id);
  98  * hash = hash_combine(hash, car_convertible);
  99  * // Now use hash as a hash of both car_id and car_convertible.
 100  * @endcode
 101  */
 102 static inline size_t hash_combine(size_t seed, size_t hash)
 103 {
 104         /*
 105          * todo: use Bob Jenkin's proper mixing hash pass:
 106          * http://burtleburtle.net/bob/c/lookup3.c
 107          */
 108         seed ^= hash + 0x9e3779b9
 109                 + ((seed << 5) | (seed >> (sizeof(size_t) * 8 - 5)));
 110         return seed;
 111 }
 112
 113 #endif