adler32.c
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adler32.c
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	/* adler32.c -- compute the Adler-32 checksum of a data stream
	* Copyright (C) 1995-1998 Mark Adler
	* For conditions of distribution and use, see copyright notice in zlib.h
	*/

	/* @(#) $Id$ */

	#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(adler, buf, len)
	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;
	}