src/util/fnv1a.h

   1 /*
   2  * Copyright © 2009,2012 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  *
  23  * Authors:
  24  *    Eric Anholt <eric@anholt.net>
  25  *
  26  */
  27
  28 #ifndef _FNV1A_H
  29 #define _FNV1A_H
  30
  31 enum {
  32    _mesa_fnv32_1a_offset_bias = 2166136261u,
  33 };
  34
  35 /**
  36  * Quick FNV-1a hash implementation based on:
  37  * http://www.isthe.com/chongo/tech/comp/fnv/
  38  *
  39  * FNV-1a is not be the best hash out there -- Jenkins's lookup3 is supposed
  40  * to be quite good, and it probably beats FNV.  But FNV has the advantage
  41  * that it involves almost no code.  For an improvement on both, see Paul
  42  * Hsieh's http://www.azillionmonkeys.com/qed/hash.html
  43  */
  44 static inline uint32_t
  45 _mesa_fnv32_1a_accumulate_block(uint32_t hash, const void *data, size_t size)
  46 {
  47    const uint8_t *bytes = (const uint8_t *)data;
  48
  49    while (size-- != 0) {
  50       hash ^= *bytes;
  51       hash = hash * 0x01000193;
  52       bytes++;
  53    }
  54
  55    return hash;
  56 }
  57
  58 #define _mesa_fnv32_1a_accumulate(hash, expr) \
  59    _mesa_fnv32_1a_accumulate_block(hash, &(expr), sizeof(expr))
  60
  61 #endif