1 /* adler32.c -- compute the Adler-32 checksum of a data stream
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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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6 /* @(#) $Id: adler32.c,v 1.1 2003/05/23 21:05:30 steveking Exp $ */
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10 #define BASE 65521L /* largest prime smaller than 65536 */
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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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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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20 /* ========================================================================= */
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21 uLong ZEXPORT adler32(adler, buf, len)
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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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30 if (buf == Z_NULL) return 1L;
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33 k = len < NMAX ? len : NMAX;
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47 return (s2 << 16) | s1;
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