| 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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| 4 | */
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| 5 |
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| 6 | /* @(#) $Id: adler32.c,v 1.1 2004/11/15 16:42:25 bird Exp $ */
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| 7 |
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| 8 | #define ZLIB_INTERNAL
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| 9 | #include "zlib.h"
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| 10 |
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| 11 | #define BASE 65521UL /* largest prime smaller than 65536 */
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| 12 | #define NMAX 5552
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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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| 14 |
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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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| 20 |
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| 21 | #ifdef NO_DIVIDE
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| 22 | # define MOD(a) \
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| 23 | do { \
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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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| 41 | } while (0)
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| 42 | #else
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| 43 | # define MOD(a) a %= BASE
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| 44 | #endif
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| 45 |
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| 46 | /* ========================================================================= */
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| 47 | uLong ZEXPORT adler32(adler, buf, len)
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| 48 | uLong adler;
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| 49 | const Bytef *buf;
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| 50 | uInt len;
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| 51 | {
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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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| 54 | int k;
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| 55 |
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| 56 | if (buf == Z_NULL) return 1L;
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| 57 |
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| 58 | while (len > 0) {
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| 59 | k = len < NMAX ? (int)len : NMAX;
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| 60 | len -= k;
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| 61 | while (k >= 16) {
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| 62 | DO16(buf);
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| 63 | buf += 16;
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| 64 | k -= 16;
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| 65 | }
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| 66 | if (k != 0) do {
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| 67 | s1 += *buf++;
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| 68 | s2 += s1;
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| 69 | } while (--k);
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| 70 | MOD(s1);
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| 71 | MOD(s2);
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| 72 | }
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| 73 | return (s2 << 16) | s1;
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| 74 | }
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