1 /* adler32.c -- compute the Adler-32 checksum of a data stream
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2 * Copyright (C) 1995-2003 Mark Adler
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3 * For conditions of distribution and use, see copyright notice in zlib.h
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8 #define ZLIB_INTERNAL
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11 #define BASE 65521UL /* largest prime smaller than 65536 */
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13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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15 #define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
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16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
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17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
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18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
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19 #define DO16(buf) DO8(buf,0); DO8(buf,8);
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24 if (a >= (BASE << 16)) a -= (BASE << 16); \
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25 if (a >= (BASE << 15)) a -= (BASE << 15); \
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26 if (a >= (BASE << 14)) a -= (BASE << 14); \
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27 if (a >= (BASE << 13)) a -= (BASE << 13); \
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28 if (a >= (BASE << 12)) a -= (BASE << 12); \
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29 if (a >= (BASE << 11)) a -= (BASE << 11); \
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30 if (a >= (BASE << 10)) a -= (BASE << 10); \
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31 if (a >= (BASE << 9)) a -= (BASE << 9); \
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32 if (a >= (BASE << 8)) a -= (BASE << 8); \
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33 if (a >= (BASE << 7)) a -= (BASE << 7); \
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34 if (a >= (BASE << 6)) a -= (BASE << 6); \
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35 if (a >= (BASE << 5)) a -= (BASE << 5); \
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36 if (a >= (BASE << 4)) a -= (BASE << 4); \
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37 if (a >= (BASE << 3)) a -= (BASE << 3); \
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38 if (a >= (BASE << 2)) a -= (BASE << 2); \
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39 if (a >= (BASE << 1)) a -= (BASE << 1); \
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40 if (a >= BASE) a -= BASE; \
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43 # define MOD(a) a %= BASE
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46 /* ========================================================================= */
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47 uLong ZEXPORT adler32(adler, buf, len)
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52 unsigned long s1 = adler & 0xffff;
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53 unsigned long s2 = (adler >> 16) & 0xffff;
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56 if (buf == Z_NULL) return 1L;
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59 k = len < NMAX ? (int)len : NMAX;
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73 return (s2 << 16) | s1;
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