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f4c6fd49 |
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 | */ |
5 | |
6 | /* @(#) $Id$ */ |
7 | |
8 | #define ZLIB_INTERNAL |
9 | #include "zlib.h" |
10 | |
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 */ |
14 | |
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); |
20 | |
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 |
45 | |
46 | /* ========================================================================= */ |
47 | uLong ZEXPORT adler32(adler, buf, len) |
48 | uLong adler; |
49 | const Bytef *buf; |
50 | uInt len; |
51 | { |
52 | unsigned long s1 = adler & 0xffff; |
53 | unsigned long s2 = (adler >> 16) & 0xffff; |
54 | int k; |
55 | |
56 | if (buf == Z_NULL) return 1L; |
57 | |
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; |
65 | } |
66 | if (k != 0) do { |
67 | s1 += *buf++; |
68 | s2 += s1; |
69 | } while (--k); |
70 | MOD(s1); |
71 | MOD(s2); |
72 | } |
73 | return (s2 << 16) | s1; |
74 | } |