/*?adler32.c?--?compute?the?Adler-32?checksum?of?a?data?stream
?*?Copyright?（C）?1995-2011?Mark?Adler
?*?For?conditions?of?distribution?and?use?see?copyright?notice?in?zlib.h
?*/

/*?@（#）?$Id$?*/

#include?“zutil.h“

#define?local?static

local?uLong?adler32_combine_?OF（（uLong?adler1?uLong?adler2?z_off64_t?len2））;

#define?base?65521??????/*?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（bufi）??{adler?+=?（buf）[i];?sum2?+=?adler;}
#define?DO2（bufi）??DO1（bufi）;?DO1（bufi+1）;
#define?DO4（bufi）??DO2（bufi）;?DO2（bufi+2）;
#define?DO8（bufi）??DO4（bufi）;?DO4（bufi+4）;
#define?DO16（buf）???DO8（buf0）;?DO8（buf8）;

/*?use?NO_DIVIDE?if?your?processor?does?not?do?division?in?hardware?--
???try?it?both?ways?to?see?which?is?faster?*/
#ifdef?NO_DIVIDE
/*?note?that?this?assumes?base?is?65521?where?65536?%?65521?==?15
???（thank?you?to?John?Reiser?for?pointing?this?out）?*/
#??define?CHOP（a）?\
????do?{?\
????????unsigned?long?tmp?=?a?>>?16;?\
????????a?&=?0xffffUL;?\
????????a?+=?（tmp?<????}?while?（0）
#??define?MOD28（a）?\
????do?{?\
????????CHOP（a）;?\
????????if?（a?>=?base）?a?-=?base;?\
????}?while?（0）
#??define?MOD（a）?\
????do?{?\
????????CHOP（a）;?\
????????MOD28（a）;?\
????}?while?（0）
#??define?MOD63（a）?\
????do?{?/*?this?assumes?a?is?not?negative?*/?\
????????z_off64_t?tmp?=?a?>>?32;?\
????????a?&=?0xffffffffL;?\
????????a?+=?（tmp?<????????tmp?=?a?>>?16;?\
????????a?&=?0xffffL;?\
????????a?+=?（tmp?<????????tmp?=?a?>>?16;?\
????????a?&=?0xffffL;?\
????????a?+=?（tmp?<????????if?（a?>=?base）?a?-=?base;?\
????}?while?（0）
#else
#??define?MOD（a）?a?%=?base
#??define?MOD28（a）?a?%=?base
#??define?MOD63（a）?a?%=?base
#endif

/*?=========================================================================?*/
uLong?ZEXPORT?adler32（adler?buf?len）
????uLong?adler;
????const?Bytef?*buf;
????uInt?len;
{
????unsigned?long?sum2;
????unsigned?n;

????/*?split?Adler-32?into?component?sums?*/
????sum2?=?（adler?>>?16）?&?0xffff;
????adler?&=?0xffff;

????/*?in?case?user?likes?doing?a?byte?at?a?time?keep?it?fast?*/
????if?（len?==?1）?{
????????adler?+=?buf[0];
????????if?（adler?>=?base）
????????????adler?-=?base;
????????sum2?+=?adler;
????????if?（sum2?>=?base）
????????????sum2?-=?base;
????????return?adler?|?（sum2?<????}

????/*?initial?Adler-32?value?（deferred?check?for?len?==?1?speed）?*/
????if?（buf?==?Z_NULL）
????????return?1L;

????/*?in?case?short?lengths?are?provided?keep?it?somewhat?fast?*/
????if?（len?????????while?（len--）?{
????????????adler?+=?*buf++;
????????????sum2?+=?adler;
????????}
????????if?（adler?>=?base）
????????????adler?-=?base;
????????MOD28（sum2）;????????????/*?only?added?so?many?base‘s?*/
????????return?adler?|?（sum2?<????}

????/*?do?length?NMAX?blocks?--?requires?just?one?modulo?operation?*/
????while?（len?>=?NMAX）?{
????????len?-=?NMAX;
????????n?=?NMAX?/?16;??????????/