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Rev | Author | Line No. | Line |
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107 | pj | 1 | /* adler32.c -- compute the Adler-32 checksum of a data stream |
2 | * Copyright (C) 1995-2002 Mark Adler |
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3 | * For conditions of distribution and use, see copyright notice in zlib.h |
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4 | */ |
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5 | |||
6 | /* @(#) $Id: adler32.c,v 1.1 2003-03-24 11:13:44 pj Exp $ */ |
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7 | |||
8 | #include "zlib.h" |
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9 | |||
10 | #define BASE 65521L /* largest prime smaller than 65536 */ |
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11 | #define NMAX 5552 |
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12 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ |
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13 | |||
14 | #define DO1(buf,i) {s1 += buf[i]; s2 += s1;} |
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15 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); |
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16 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); |
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17 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); |
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18 | #define DO16(buf) DO8(buf,0); DO8(buf,8); |
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19 | |||
20 | /* ========================================================================= */ |
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21 | uLong ZEXPORT adler32(adler, buf, len) |
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22 | uLong adler; |
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23 | const Bytef *buf; |
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24 | uInt len; |
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25 | { |
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26 | unsigned long s1 = adler & 0xffff; |
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27 | unsigned long s2 = (adler >> 16) & 0xffff; |
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28 | int k; |
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29 | |||
30 | if (buf == Z_NULL) return 1L; |
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31 | |||
32 | while (len > 0) { |
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33 | k = len < NMAX ? len : NMAX; |
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34 | len -= k; |
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35 | while (k >= 16) { |
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36 | DO16(buf); |
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37 | buf += 16; |
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38 | k -= 16; |
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39 | } |
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40 | if (k != 0) do { |
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41 | s1 += *buf++; |
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42 | s2 += s1; |
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43 | } while (--k); |
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44 | s1 %= BASE; |
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45 | s2 %= BASE; |
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46 | } |
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47 | return (s2 << 16) | s1; |
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48 | } |