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49 lines
1.1 KiB
49 lines
1.1 KiB
2 months ago
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/*
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* adler32.c -- compute the Adler-32 checksum of a data stream
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*
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* Copyright (C) 1995--2003 Mark Adler
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*
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* Taken from zlib-1.2.1 and adjusted by Robert Spalek. For conditions of
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* distribution and use, see copyright notice in zlib.h.
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*/
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#include <ucw/lib.h>
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#include <ucw/lizard.h>
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#define BASE 65521UL /* largest prime smaller than 65536 */
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#define NMAX 5552 /* 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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#define MOD(a) a %= BASE
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uint
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adler32_update(uint adler, const byte *buf, uint len)
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{
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uint s1 = adler & 0xffff;
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uint s2 = (adler >> 16) & 0xffff;
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int k;
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if (!buf) return 1L;
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while (len > 0) {
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k = len < NMAX ? (int)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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MOD(s1);
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MOD(s2);
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}
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return (s2 << 16) | s1;
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}
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