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SDL_crc32.c (1706B)

      1 /*
      2   Simple DirectMedia Layer
      3   Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>
      4 
      5   This software is provided 'as-is', without any express or implied
      6   warranty.  In no event will the authors be held liable for any damages
      7   arising from the use of this software.
      8 
      9   Permission is granted to anyone to use this software for any purpose,
     10   including commercial applications, and to alter it and redistribute it
     11   freely, subject to the following restrictions:
     12 
     13   1. The origin of this software must not be misrepresented; you must not
     14      claim that you wrote the original software. If you use this software
     15      in a product, an acknowledgment in the product documentation would be
     16      appreciated but is not required.
     17   2. Altered source versions must be plainly marked as such, and must not be
     18      misrepresented as being the original software.
     19   3. This notice may not be removed or altered from any source distribution.
     20 */
     21 #include "../SDL_internal.h"
     22 
     23 #include "SDL_stdinc.h"
     24 
     25 
     26 /* Public domain CRC implementation adapted from:
     27    http://home.thep.lu.se/~bjorn/crc/crc32_simple.c
     28 */
     29 /* NOTE: DO NOT CHANGE THIS ALGORITHM
     30    There is code that relies on this in the joystick code
     31 */
     32 
     33 static Uint32 crc32_for_byte(Uint32 r)
     34 {
     35     int i;
     36     for(i = 0; i < 8; ++i) {
     37         r = (r & 1? 0: (Uint32)0xEDB88320L) ^ r >> 1;
     38     }
     39     return r ^ (Uint32)0xFF000000L;
     40 }
     41 
     42 Uint32 SDL_crc32(Uint32 crc, const void *data, size_t len)
     43 {
     44     /* As an optimization we can precalculate a 256 entry table for each byte */
     45     size_t i;
     46     for(i = 0; i < len; ++i) {
     47         crc = crc32_for_byte((Uint8)crc ^ ((const Uint8*)data)[i]) ^ crc >> 8;
     48     }
     49     return crc;
     50 }
     51 
     52 /* vi: set ts=4 sw=4 expandtab: */