Atlas - SDL_crc32.c
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[FILE BEGIN]
1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2025 Sam Lantinga <[email protected]>
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/* Public domain CRC implementation adapted from:
24   http://home.thep.lu.se/~bjorn/crc/crc32_simple.c
25
26   This algorithm is compatible with the 32-bit CRC described here:
27   https://www.lammertbies.nl/comm/info/crc-calculation
28*/
29/* NOTE: DO NOT CHANGE THIS ALGORITHM
30   There is code that relies on this in the joystick code
31*/
32
33static 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
42Uint32 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
[FILE END]
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