/* 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 | |
*/ | |
/* @(#) $Id$ */ | |
#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; | |
} |