1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2002 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6 /* @(#) $Id$ */
7
8 #include "zlib.h"
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 /* ========================================================================= */
adler32(uLong adler,const Bytef * buf,uInt len)21 ZEXPORT(uLong) adler32( /* adler, buf, len) */
22 uLong adler,
23 const Bytef *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 buf += 16;
38 k -= 16;
39 }
40 if (k != 0) do {
41 s1 += *buf++;
42 s2 += s1;
43 } while (--k);
44 s1 %= BASE;
45 s2 %= BASE;
46 }
47 return (s2 << 16) | s1;
48 }
49