58 lines
1.8 KiB
C
58 lines
1.8 KiB
C
/*
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Simple DirectMedia Layer
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Copyright (C) 1997-2022 Sam Lantinga <slouken@libsdl.org>
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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#include "../SDL_internal.h"
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#include "SDL_stdinc.h"
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/* Public domain CRC implementation adapted from:
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http://home.thep.lu.se/~bjorn/crc/crc32_simple.c
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This algorithm is compatible with the 16-bit CRC described here:
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https://www.lammertbies.nl/comm/info/crc-calculation
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*/
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/* NOTE: DO NOT CHANGE THIS ALGORITHM
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There is code that relies on this in the joystick code
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*/
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static Uint16 crc16_for_byte(Uint8 r)
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{
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Uint16 crc = 0;
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int i;
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for (i = 0; i < 8; ++i) {
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crc = ((crc ^ r) & 1? 0xA001 : 0) ^ crc >> 1;
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r >>= 1;
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}
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return crc;
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}
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Uint16 SDL_crc16(Uint16 crc, const void *data, size_t len)
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{
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/* As an optimization we can precalculate a 256 entry table for each byte */
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size_t i;
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for(i = 0; i < len; ++i) {
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crc = crc16_for_byte((Uint8)crc ^ ((const Uint8*)data)[i]) ^ crc >> 8;
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}
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return crc;
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}
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/* vi: set ts=4 sw=4 expandtab: */
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