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[official-gcc.git] / zlib / adler32.c
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1 /* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2003 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
6 /* @(#) $Id: adler32.c,v 1.1.1.2 2002/03/11 21:53:23 tromey Exp $ */
8 #define ZLIB_INTERNAL
9 #include "zlib.h"
11 #define BASE 65521UL /* largest prime smaller than 65536 */
12 #define NMAX 5552
13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
15 #define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
19 #define DO16(buf) DO8(buf,0); DO8(buf,8);
21 #ifdef NO_DIVIDE
22 # define MOD(a) \
23 do { \
24 if (a >= (BASE << 16)) a -= (BASE << 16); \
25 if (a >= (BASE << 15)) a -= (BASE << 15); \
26 if (a >= (BASE << 14)) a -= (BASE << 14); \
27 if (a >= (BASE << 13)) a -= (BASE << 13); \
28 if (a >= (BASE << 12)) a -= (BASE << 12); \
29 if (a >= (BASE << 11)) a -= (BASE << 11); \
30 if (a >= (BASE << 10)) a -= (BASE << 10); \
31 if (a >= (BASE << 9)) a -= (BASE << 9); \
32 if (a >= (BASE << 8)) a -= (BASE << 8); \
33 if (a >= (BASE << 7)) a -= (BASE << 7); \
34 if (a >= (BASE << 6)) a -= (BASE << 6); \
35 if (a >= (BASE << 5)) a -= (BASE << 5); \
36 if (a >= (BASE << 4)) a -= (BASE << 4); \
37 if (a >= (BASE << 3)) a -= (BASE << 3); \
38 if (a >= (BASE << 2)) a -= (BASE << 2); \
39 if (a >= (BASE << 1)) a -= (BASE << 1); \
40 if (a >= BASE) a -= BASE; \
41 } while (0)
42 #else
43 # define MOD(a) a %= BASE
44 #endif
46 /* ========================================================================= */
47 uLong ZEXPORT adler32(adler, buf, len)
48 uLong adler;
49 const Bytef *buf;
50 uInt len;
52 unsigned long s1 = adler & 0xffff;
53 unsigned long s2 = (adler >> 16) & 0xffff;
54 int k;
56 if (buf == Z_NULL) return 1L;
58 while (len > 0) {
59 k = len < NMAX ? (int)len : NMAX;
60 len -= k;
61 while (k >= 16) {
62 DO16(buf);
63 buf += 16;
64 k -= 16;
66 if (k != 0) do {
67 s1 += *buf++;
68 s2 += s1;
69 } while (--k);
70 MOD(s1);
71 MOD(s2);
73 return (s2 << 16) | s1;