/* 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(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;
}
