74 lines
2.2 KiB
C
Executable file
74 lines
2.2 KiB
C
Executable file
/* 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;
|
|
}
|