[562] | 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.cc,v 1.1 2005/05/12 21:04:53 duns 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(uLong adler, const Bytef *buf, uInt len) |
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| 48 | { |
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| 49 | unsigned long s1 = adler & 0xffff; |
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| 50 | unsigned long s2 = (adler >> 16) & 0xffff; |
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| 51 | int k; |
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| 52 | |
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| 53 | if (buf == Z_NULL) return 1L; |
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| 54 | |
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| 55 | while (len > 0) { |
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| 56 | k = len < NMAX ? (int)len : NMAX; |
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| 57 | len -= k; |
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| 58 | while (k >= 16) { |
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| 59 | DO16(buf); |
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| 60 | buf += 16; |
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| 61 | k -= 16; |
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| 62 | } |
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| 63 | if (k != 0) do { |
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| 64 | s1 += *buf++; |
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| 65 | s2 += s1; |
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| 66 | } while (--k); |
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| 67 | MOD(s1); |
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| 68 | MOD(s2); |
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| 69 | } |
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| 70 | return (s2 << 16) | s1; |
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| 71 | } |
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