source/lib/fnv_hash.cpp

   1 /* Copyright (C) 2021 Wildfire Games.
   2  *
   3  * Permission is hereby granted, free of charge, to any person obtaining
   4  * a copy of this software and associated documentation files (the
   5  * "Software"), to deal in the Software without restriction, including
   6  * without limitation the rights to use, copy, modify, merge, publish,
   7  * distribute, sublicense, and/or sell copies of the Software, and to
   8  * permit persons to whom the Software is furnished to do so, subject to
   9  * the following conditions:
  10  *
  11  * The above copyright notice and this permission notice shall be included
  12  * in all copies or substantial portions of the Software.
  13  *
  14  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  15  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  16  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  17  * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
  18  * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  19  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  20  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  21  */
  22
  23 #include "precompiled.h"
  24
  25 #include "lib/fnv_hash.h"
  26
  27 // FNV1-A hash - good for strings.
  28 // if len = 0 (default), treat buf as a C-string;
  29 // otherwise, hash <len> bytes of buf.
  30 u32 fnv_hash(const void* buf, size_t len)
  31 {
  32         u32 h = 0x811c9dc5u;
  33         // give distinct values for different length 0 buffers.
  34         // value taken from FNV; it has no special significance.
  35
  36         const u8* p = (const u8*)buf;
  37
  38         // expected case: string
  39         if(!len)
  40         {
  41                 while(*p)
  42                 {
  43                         h ^= *p++;
  44                         h *= 0x01000193u;
  45                 }
  46         }
  47         else
  48         {
  49                 size_t bytes_left = len;
  50                 while(bytes_left != 0)
  51                 {
  52                         h ^= *p++;
  53                         h *= 0x01000193u;
  54
  55                         bytes_left--;
  56                 }
  57         }
  58
  59         return h;
  60 }
  61
  62 // FNV1-A hash - good for strings.
  63 // if len = 0 (default), treat buf as a C-string;
  64 // otherwise, hash <len> bytes of buf.
  65 u64 fnv_hash64(const void* buf, size_t len)
  66 {
  67         u64 h = 0xCBF29CE484222325ull;
  68         // give distinct values for different length 0 buffers.
  69         // value taken from FNV; it has no special significance.
  70
  71         const u8* p = (const u8*)buf;
  72
  73         // expected case: string
  74         if(!len)
  75         {
  76                 while(*p)
  77                 {
  78                         h ^= *p++;
  79                         h *= 0x100000001B3ull;
  80                 }
  81         }
  82         else
  83         {
  84                 size_t bytes_left = len;
  85                 while(bytes_left != 0)
  86                 {
  87                         h ^= *p++;
  88                         h *= 0x100000001B3ull;
  89
  90                         bytes_left--;
  91                 }
  92         }
  93
  94         return h;
  95 }