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

 * Copyright (C) 1995-2003 Mark Adler

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

 */

/* @(#) $Id: adler32.c,v 1.1 2003/12/07 05:29:20 icculus Exp $ */

#define ZLIB_INTERNAL

#include "zlib.h"

#define BASE 65521UL    /* 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);

#ifdef NO_DIVIDE

#  define MOD(a) \

    do { \

        if (a >= (BASE << 16)) a -= (BASE << 16); \

        if (a >= (BASE << 15)) a -= (BASE << 15); \

        if (a >= (BASE << 14)) a -= (BASE << 14); \

        if (a >= (BASE << 13)) a -= (BASE << 13); \

        if (a >= (BASE << 12)) a -= (BASE << 12); \

        if (a >= (BASE << 11)) a -= (BASE << 11); \

        if (a >= (BASE << 10)) a -= (BASE << 10); \

        if (a >= (BASE << 9)) a -= (BASE << 9); \

        if (a >= (BASE << 8)) a -= (BASE << 8); \

        if (a >= (BASE << 7)) a -= (BASE << 7); \

        if (a >= (BASE << 6)) a -= (BASE << 6); \

        if (a >= (BASE << 5)) a -= (BASE << 5); \

        if (a >= (BASE << 4)) a -= (BASE << 4); \

        if (a >= (BASE << 3)) a -= (BASE << 3); \

        if (a >= (BASE << 2)) a -= (BASE << 2); \

        if (a >= (BASE << 1)) a -= (BASE << 1); \

        if (a >= BASE) a -= BASE; \

    } while (0)

#else

#  define MOD(a) a %= BASE

#endif

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

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 ? (int)len : NMAX;

        len -= k;

        while (k >= 16) {

            DO16(buf);

            buf += 16;

            k -= 16;

        }

        if (k != 0) do {

            s1 += *buf++;

            s2 += s1;

        } while (--k);

        MOD(s1);

        MOD(s2);

    }

    return (s2 << 16) | s1;

}