sl@0: /* adler32.c -- compute the Adler-32 checksum of a data stream
sl@0:  * Copyright (C) 1995-1998 Mark Adler
sl@0:  * For conditions of distribution and use, see copyright notice in zlib.h 
sl@0:  */
sl@0: 
sl@0: /* @(#) $Id$ */
sl@0: 
sl@0: #include "zlib.h"
sl@0: 
sl@0: #define BASE 65521L /* largest prime smaller than 65536 */
sl@0: #define NMAX 5552
sl@0: /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
sl@0: 
sl@0: #define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
sl@0: #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
sl@0: #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
sl@0: #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
sl@0: #define DO16(buf)   DO8(buf,0); DO8(buf,8);
sl@0: 
sl@0: /* ========================================================================= */
sl@0: uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)
sl@0: {
sl@0:     unsigned long s1 = adler & 0xffff;
sl@0:     unsigned long s2 = (adler >> 16) & 0xffff;
sl@0:     int k;
sl@0: 
sl@0:     if (buf == Z_NULL) return 1L;
sl@0: 
sl@0:     while (len > 0) {
sl@0:         k = len < NMAX ? len : NMAX;
sl@0:         len -= k;
sl@0:         while (k >= 16) {
sl@0:             DO16(buf);
sl@0: 	    buf += 16;
sl@0:             k -= 16;
sl@0:         }
sl@0:         if (k != 0) do {
sl@0:             s1 += *buf++;
sl@0: 	    s2 += s1;
sl@0:         } while (--k);
sl@0:         s1 %= BASE;
sl@0:         s2 %= BASE;
sl@0:     }
sl@0:     return (s2 << 16) | s1;
sl@0: }