78 lines
2.1 KiB
C
78 lines
2.1 KiB
C
/*
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* Adler-32 checksum
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*
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* Copyright (c) 2003 by Joergen Ibsen / Jibz
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* All Rights Reserved
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*
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* http://www.ibsensoftware.com/
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*
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* This software is provided 'as-is', without any express
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* or implied warranty. In no event will the authors be
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* held liable for any damages arising from the use of
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* this software.
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*
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* Permission is granted to anyone to use this software
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* for any purpose, including commercial applications,
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* and to alter it and redistribute it freely, subject to
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* the following restrictions:
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*
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* 1. The origin of this software must not be
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* misrepresented; you must not claim that you
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* wrote the original software. If you use this
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* software in a product, an acknowledgment in
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* the product documentation would be appreciated
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* but is not required.
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*
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* 2. Altered source versions must be plainly marked
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* as such, and must not be misrepresented as
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* being the original software.
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*
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* 3. This notice may not be removed or altered from
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* any source distribution.
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*/
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/*
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* Adler-32 algorithm taken from the zlib source, which is
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* Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
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*/
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#include "tinf.h"
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#define A32_BASE 65521
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#define A32_NMAX 5552
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unsigned int tinf_adler32(const void *data, unsigned int length)
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{
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const unsigned char *buf = (const unsigned char *)data;
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unsigned int s1 = 1;
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unsigned int s2 = 0;
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while (length > 0)
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{
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int k = length < A32_NMAX ? length : A32_NMAX;
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int i;
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for (i = k / 16; i; --i, buf += 16)
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{
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s1 += buf[0]; s2 += s1; s1 += buf[1]; s2 += s1;
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s1 += buf[2]; s2 += s1; s1 += buf[3]; s2 += s1;
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s1 += buf[4]; s2 += s1; s1 += buf[5]; s2 += s1;
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s1 += buf[6]; s2 += s1; s1 += buf[7]; s2 += s1;
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s1 += buf[8]; s2 += s1; s1 += buf[9]; s2 += s1;
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s1 += buf[10]; s2 += s1; s1 += buf[11]; s2 += s1;
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s1 += buf[12]; s2 += s1; s1 += buf[13]; s2 += s1;
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s1 += buf[14]; s2 += s1; s1 += buf[15]; s2 += s1;
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}
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for (i = k % 16; i; --i) { s1 += *buf++; s2 += s1; }
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s1 %= A32_BASE;
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s2 %= A32_BASE;
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length -= k;
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}
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return (s2 << 16) | s1;
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}
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