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1/* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-1998 Mark Adler
e6ebb514 3 * For conditions of distribution and use, see copyright notice in zlib.h
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4 */
5
6/* @(#) $Id$ */
7
1f0299c1 8#include "../zlib/zlib.h"
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9
10#define BASE 65521L /* largest prime smaller than 65536 */
11#define NMAX 5552
12/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13
14#define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
15#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
16#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
17#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
18#define DO16(buf) DO8(buf,0); DO8(buf,8);
19
20/* ========================================================================= */
75bce3ad 21#if defined(__VISAGECPP__) /* Visualage can't handle this antiquated interface */
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22uLong ZEXPORT adler32 (uLong adler, const Bytef* buf, uInt len)
23#else
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24uLong ZEXPORT adler32(adler, buf, len)
25 uLong adler;
26 const Bytef *buf;
27 uInt len;
e6ebb514 28#endif
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29{
30 unsigned long s1 = adler & 0xffff;
31 unsigned long s2 = (adler >> 16) & 0xffff;
32 int k;
33
34 if (buf == Z_NULL) return 1L;
35
36 while (len > 0) {
37 k = len < NMAX ? len : NMAX;
38 len -= k;
39 while (k >= 16) {
40 DO16(buf);
41 buf += 16;
42 k -= 16;
43 }
44 if (k != 0) do {
45 s1 += *buf++;
46 s2 += s1;
47 } while (--k);
48 s1 %= BASE;
49 s2 %= BASE;
50 }
51 return (s2 << 16) | s1;
52}