1 | /* |
2 | Simple DirectMedia Layer |
3 | Copyright (C) 1997-2025 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 | /* 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 16-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 | |
33 | static Uint16 crc16_for_byte(Uint8 r) |
34 | { |
35 | Uint16 crc = 0; |
36 | int i; |
37 | for (i = 0; i < 8; ++i) { |
38 | crc = ((crc ^ r) & 1 ? 0xA001 : 0) ^ crc >> 1; |
39 | r >>= 1; |
40 | } |
41 | return crc; |
42 | } |
43 | |
44 | Uint16 SDL_crc16(Uint16 crc, const void *data, size_t len) |
45 | { |
46 | // As an optimization we can precalculate a 256 entry table for each byte |
47 | size_t i; |
48 | for (i = 0; i < len; ++i) { |
49 | crc = crc16_for_byte((Uint8)crc ^ ((const Uint8 *)data)[i]) ^ crc >> 8; |
50 | } |
51 | return crc; |
52 | } |
53 | |