/* 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;

 }