150 lines
4.6 KiB
C
150 lines
4.6 KiB
C
/* adler32.c -- compute the Adler-32 checksum of a data stream
|
|
* Copyright (C) 1995-2004 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) {adler += (buf)[i]; sum2 += adler;}
|
|
#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);
|
|
|
|
/* use NO_DIVIDE if your processor does not do division in hardware */
|
|
#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)
|
|
# define MOD4(a) \
|
|
do { \
|
|
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
|
|
# define MOD4(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 << 16);
|
|
}
|
|
|
|
/* 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 < 16) {
|
|
while (len--) {
|
|
adler += *buf++;
|
|
sum2 += adler;
|
|
}
|
|
if (adler >= BASE)
|
|
adler -= BASE;
|
|
MOD4(sum2); /* only added so many BASE's */
|
|
return adler | (sum2 << 16);
|
|
}
|
|
|
|
/* do length NMAX blocks -- requires just one modulo operation */
|
|
while (len >= NMAX) {
|
|
len -= NMAX;
|
|
n = NMAX / 16; /* NMAX is divisible by 16 */
|
|
do {
|
|
DO16(buf); /* 16 sums unrolled */
|
|
buf += 16;
|
|
} while (--n);
|
|
MOD(adler);
|
|
MOD(sum2);
|
|
}
|
|
|
|
/* do remaining bytes (less than NMAX, still just one modulo) */
|
|
if (len) { /* avoid modulos if none remaining */
|
|
while (len >= 16) {
|
|
len -= 16;
|
|
DO16(buf);
|
|
buf += 16;
|
|
}
|
|
while (len--) {
|
|
adler += *buf++;
|
|
sum2 += adler;
|
|
}
|
|
MOD(adler);
|
|
MOD(sum2);
|
|
}
|
|
|
|
/* return recombined sums */
|
|
return adler | (sum2 << 16);
|
|
}
|
|
|
|
/* ========================================================================= */
|
|
uLong ZEXPORT adler32_combine(adler1, adler2, len2)
|
|
uLong adler1;
|
|
uLong adler2;
|
|
z_off_t len2;
|
|
{
|
|
unsigned long sum1;
|
|
unsigned long sum2;
|
|
unsigned rem;
|
|
|
|
/* the derivation of this formula is left as an exercise for the reader */
|
|
rem = (unsigned)(len2 % BASE);
|
|
sum1 = adler1 & 0xffff;
|
|
sum2 = rem * sum1;
|
|
MOD(sum2);
|
|
sum1 += (adler2 & 0xffff) + BASE - 1;
|
|
sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
|
|
if (sum1 > BASE) sum1 -= BASE;
|
|
if (sum1 > BASE) sum1 -= BASE;
|
|
if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
|
|
if (sum2 > BASE) sum2 -= BASE;
|
|
return sum1 | (sum2 << 16);
|
|
}
|