/* 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: adler32.c,v 1.2 2002/03/13 13:17:02 mpritchett Exp $ */

#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 */


/* ========================================================================= */
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) {
            int r=0;
            while (r < 16)
            {
              s1+=buf[r];
              s2+=s1;
              r++;
            }
			      buf += 16;
            k -= 16;
        }
        if (k != 0) do {
            s1 += *buf++;
	          s2 += s1;
        } while (--k);
        s1 %= BASE;
        s2 %= BASE;
    }
    return (s2 << 16) | s1;
}