1			/* adler32.c -- compute the Adler-32 checksum of a data stream
     2			 * Copyright (C) 1995-2003 Mark Adler
     3			 * For conditions of distribution and use, see copyright notice in zlib.h
     4			 */
     5			
     6			/* @(#) $Id$ */
     7			
     8			#define ZLIB_INTERNAL
     9			#include "zlib.h"
    10			
    11			#define BASE 65521UL    /* largest prime smaller than 65536 */
    12			#define NMAX 5552
    13			/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
    14			
    15			#define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
    16			#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
    17			#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
    18			#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
    19			#define DO16(buf)   DO8(buf,0); DO8(buf,8);
    20			
    21			#ifdef NO_DIVIDE
    22			#  define MOD(a) \
    23			    do { \
    24			        if (a >= (BASE << 16)) a -= (BASE << 16); \
    25			        if (a >= (BASE << 15)) a -= (BASE << 15); \
    26			        if (a >= (BASE << 14)) a -= (BASE << 14); \
    27			        if (a >= (BASE << 13)) a -= (BASE << 13); \
    28			        if (a >= (BASE << 12)) a -= (BASE << 12); \
    29			        if (a >= (BASE << 11)) a -= (BASE << 11); \
    30			        if (a >= (BASE << 10)) a -= (BASE << 10); \
    31			        if (a >= (BASE << 9)) a -= (BASE << 9); \
    32			        if (a >= (BASE << 8)) a -= (BASE << 8); \
    33			        if (a >= (BASE << 7)) a -= (BASE << 7); \
    34			        if (a >= (BASE << 6)) a -= (BASE << 6); \
    35			        if (a >= (BASE << 5)) a -= (BASE << 5); \
    36			        if (a >= (BASE << 4)) a -= (BASE << 4); \
    37			        if (a >= (BASE << 3)) a -= (BASE << 3); \
    38			        if (a >= (BASE << 2)) a -= (BASE << 2); \
    39			        if (a >= (BASE << 1)) a -= (BASE << 1); \
    40			        if (a >= BASE) a -= BASE; \
    41			    } while (0)
    42			#else
    43			#  define MOD(a) a %= BASE
    44			#endif
    45			
    46			/* ========================================================================= */
    47			uLong ZEXPORT adler32(adler, buf, len)
    48			    uLong adler;
    49			    const Bytef *buf;
    50			    uInt len;
    51	         278    {
    52	         278        unsigned long s1 = adler & 0xffff;
    53	         278        unsigned long s2 = (adler >> 16) & 0xffff;
    54	         278        int k;
    55			
    56	         278        if (buf == Z_NULL) return 1L;
    57			
    58	         352        while (len > 0) {
    59	         203            k = len < NMAX ? (int)len : NMAX;
    60	         203            len -= k;
    61	       24146            while (k >= 16) {
    62	       23943                DO16(buf);
    63	       23943                buf += 16;
    64	       23943                k -= 16;
    65			        }
    66	         203            if (k != 0) do {
    67	         556                s1 += *buf++;
    68	         556                s2 += s1;
    69	         556            } while (--k);
    70	         203            MOD(s1);
    71	         203            MOD(s2);
    72			    }
    73	         149        return (s2 << 16) | s1;
    74			}