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47 lines
1.1 KiB
47 lines
1.1 KiB
13 years ago
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/* adler32.c -- compute the Adler-32 checksum of a data stream
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* Copyright (C) 1995 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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*/
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/* $Id: adler32.c,v 1.5 1995/04/14 14:49:51 jloup Exp $ */
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#include "zutil.h"
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#define BASE 65521 /* largest prime smaller than 65536 */
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#define NMAX 5552
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/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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#define DO1(buf) {s1 += *buf++; s2 += s1;}
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#define DO2(buf) DO1(buf); DO1(buf);
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#define DO4(buf) DO2(buf); DO2(buf);
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#define DO8(buf) DO4(buf); DO4(buf);
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#define DO16(buf) DO8(buf); DO8(buf);
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/* ========================================================================= */
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uLong adler32(adler, buf, len)
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uLong adler;
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Byte *buf;
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uInt len;
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{
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unsigned long s1 = adler & 0xffff;
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unsigned long s2 = (adler >> 16) & 0xffff;
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int k;
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if (buf == Z_NULL) return 1L;
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while (len > 0) {
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k = len < NMAX ? len : NMAX;
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len -= k;
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while (k >= 16) {
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DO16(buf);
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k -= 16;
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}
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if (k != 0) do {
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DO1(buf);
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} while (--k);
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s1 %= BASE;
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s2 %= BASE;
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}
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return (s2 << 16) | s1;
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}
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