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comparison zlib/adler32.c @ 3:5a977ccbc7a9 default tip

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author darius
date Sat, 06 Dec 1997 05:41:29 +0000
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2:fba0b6e6cdc7 3:5a977ccbc7a9
1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6 /* $Id: adler32.c,v 1.1.1.1 1997/12/06 05:41:35 darius Exp $ */
7
8 #include "zutil.h"
9
10 #define BASE 65521 /* 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) {s1 += *buf++; s2 += s1;}
15 #define DO2(buf) DO1(buf); DO1(buf);
16 #define DO4(buf) DO2(buf); DO2(buf);
17 #define DO8(buf) DO4(buf); DO4(buf);
18 #define DO16(buf) DO8(buf); DO8(buf);
19
20 /* ========================================================================= */
21 uLong adler32(adler, buf, len)
22 uLong adler;
23 Byte *buf;
24 uInt len;
25 {
26 unsigned long s1 = adler & 0xffff;
27 unsigned long s2 = (adler >> 16) & 0xffff;
28 int k;
29
30 if (buf == Z_NULL) return 1L;
31
32 while (len > 0) {
33 k = len < NMAX ? len : NMAX;
34 len -= k;
35 while (k >= 16) {
36 DO16(buf);
37 k -= 16;
38 }
39 if (k != 0) do {
40 DO1(buf);
41 } while (--k);
42 s1 %= BASE;
43 s2 %= BASE;
44 }
45 return (s2 << 16) | s1;
46 }