mirror of
git://gcc.gnu.org/git/gcc.git
synced 2024-12-27 08:59:10 +08:00
49 lines
1.3 KiB
C
49 lines
1.3 KiB
C
/* adler32.c -- compute the Adler-32 checksum of a data stream
|
|
* Copyright (C) 1995-2002 Mark Adler
|
|
* For conditions of distribution and use, see copyright notice in zlib.h
|
|
*/
|
|
|
|
/* @(#) $Id: adler32.c,v 1.1.1.2 2002/03/11 21:53:23 tromey Exp $ */
|
|
|
|
#include "zlib.h"
|
|
|
|
#define BASE 65521L /* 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);
|
|
|
|
/* ========================================================================= */
|
|
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 ? len : NMAX;
|
|
len -= k;
|
|
while (k >= 16) {
|
|
DO16(buf);
|
|
buf += 16;
|
|
k -= 16;
|
|
}
|
|
if (k != 0) do {
|
|
s1 += *buf++;
|
|
s2 += s1;
|
|
} while (--k);
|
|
s1 %= BASE;
|
|
s2 %= BASE;
|
|
}
|
|
return (s2 << 16) | s1;
|
|
}
|