/* 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 | |
*/ | |
/* @(#) $Id$ */ | |
#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); | |
/* ========================================================================= */ | |
ZEXPORT(uLong) 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; | |
} |