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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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22 | uLong ZEXPORT adler32 (uLong adler, const Bytef* buf, uInt len) |
23 | #else | |
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24 | uLong 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 | } |