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48 lines
1.2 KiB
48 lines
1.2 KiB
/* adler32.c -- compute the Adler-32 checksum of a data stream |
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* Copyright (C) 1995-1998 Mark Adler |
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* For conditions of distribution and use, see copyright notice in zlib.h |
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*/ |
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/* @(#) $Id$ */ |
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#include "zlib.h" |
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#define BASE 65521L /* largest prime smaller than 65536 */ |
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#define NMAX 5552 |
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/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ |
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#define DO1(buf,i) {s1 += buf[i]; s2 += s1;} |
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#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); |
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#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); |
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#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); |
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#define DO16(buf) DO8(buf,0); DO8(buf,8); |
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/* ========================================================================= */ |
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uLong ZEXPORT adler32(adler, buf, len) |
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uLong adler; |
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const Bytef *buf; |
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uInt len; |
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{ |
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unsigned long s1 = adler & 0xffff; |
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unsigned long s2 = (adler >> 16) & 0xffff; |
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int k; |
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if (buf == Z_NULL) return 1L; |
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while (len > 0) { |
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k = len < NMAX ? len : NMAX; |
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len -= k; |
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while (k >= 16) { |
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DO16(buf); |
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buf += 16; |
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k -= 16; |
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} |
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if (k != 0) do { |
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s1 += *buf++; |
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s2 += s1; |
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} while (--k); |
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s1 %= BASE; |
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s2 %= BASE; |
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} |
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return (s2 << 16) | s1; |
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}
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