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3
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1 /* adler32.c -- compute the Adler-32 checksum of a data stream
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2 * Copyright (C) 1995 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
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6 /* $Id: adler32.c,v 1.1.1.1 1997/12/06 05:41:35 darius Exp $ */
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7
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8 #include "zutil.h"
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9
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10 #define BASE 65521 /* 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
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14 #define DO1(buf) {s1 += *buf++; s2 += s1;}
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15 #define DO2(buf) DO1(buf); DO1(buf);
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16 #define DO4(buf) DO2(buf); DO2(buf);
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17 #define DO8(buf) DO4(buf); DO4(buf);
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18 #define DO16(buf) DO8(buf); DO8(buf);
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19
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20 /* ========================================================================= */
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21 uLong adler32(adler, buf, len)
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22 uLong adler;
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23 Byte *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
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30 if (buf == Z_NULL) return 1L;
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31
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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 k -= 16;
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38 }
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39 if (k != 0) do {
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40 DO1(buf);
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41 } while (--k);
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42 s1 %= BASE;
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43 s2 %= BASE;
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44 }
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45 return (s2 << 16) | s1;
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46 }
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