zfs-win/zlib/adler32.cpp at main · dominicusin/zfs-win

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/* adler32.c -- compute the Adler-32 checksum of a data stream

* For conditions of distribution and use, see copyright notice in zlib.h

/* @(#) $Id: adler32.c 126 2003-11-09 01:53:27Z gabest $ */

#include "stdafx.h"

#include "zlib.h"

#define BASE 65521L /* largest prime smaller than 65536 */

#define NMAX 5552

/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */

#define DO1(buf,i) {s1 += buf[i]; s2 += s1;}

#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);

#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);

#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);

#define DO16(buf) DO8(buf,0); DO8(buf,8);

/* ========================================================================= */

uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)

{

unsigned long s1 = adler & 0xffff;

unsigned long s2 = (adler >> 16) & 0xffff;

int k;

if (buf == Z_NULL) return 1L;

while (len > 0) {

k = len < NMAX ? len : NMAX;

len -= k;

while (k >= 16) {

DO16(buf);

buf += 16;

k -= 16;

}

if (k != 0) do {

s1 += *buf++;

s2 += s1;

} while (--k);

s1 %= BASE;

s2 %= BASE;

}

return (s2 << 16) | s1;

}