/* adler32.c -- compute the Adler-32 checksum of a data stream | |
* Copyright (C) 1995-2011 Mark Adler | |
* For conditions of distribution and use, see copyright notice in zlib.h | |
*/ | |
/* @(#) $Id$ */ | |
#include "zutil.h" | |
#define local static | |
local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); | |
#define BASE 65521 /* 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 -- | |
try it both ways to see which is faster */ | |
#ifdef NO_DIVIDE | |
/* note that this assumes BASE is 65521, where 65536 % 65521 == 15 | |
(thank you to John Reiser for pointing this out) */ | |
# define CHOP(a) \ | |
do { \ | |
unsigned long tmp = a >> 16; \ | |
a &= 0xffffUL; \ | |
a += (tmp << 4) - tmp; \ | |
} while (0) | |
# define MOD28(a) \ | |
do { \ | |
CHOP(a); \ | |
if (a >= BASE) a -= BASE; \ | |
} while (0) | |
# define MOD(a) \ | |
do { \ | |
CHOP(a); \ | |
MOD28(a); \ | |
} while (0) | |
# define MOD63(a) \ | |
do { /* this assumes a is not negative */ \ | |
z_off64_t tmp = a >> 32; \ | |
a &= 0xffffffffL; \ | |
a += (tmp << 8) - (tmp << 5) + tmp; \ | |
tmp = a >> 16; \ | |
a &= 0xffffL; \ | |
a += (tmp << 4) - tmp; \ | |
tmp = a >> 16; \ | |
a &= 0xffffL; \ | |
a += (tmp << 4) - tmp; \ | |
if (a >= BASE) a -= BASE; \ | |
} while (0) | |
#else | |
# define MOD(a) a %= BASE | |
# define MOD28(a) a %= BASE | |
# define MOD63(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; | |
MOD28(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); | |
} | |
/* ========================================================================= */ | |
local uLong adler32_combine_(adler1, adler2, len2) | |
uLong adler1; | |
uLong adler2; | |
z_off64_t len2; | |
{ | |
unsigned long sum1; | |
unsigned long sum2; | |
unsigned rem; | |
/* for negative len, return invalid adler32 as a clue for debugging */ | |
if (len2 < 0) | |
return 0xffffffffUL; | |
/* the derivation of this formula is left as an exercise for the reader */ | |
MOD63(len2); /* assumes len2 >= 0 */ | |
rem = (unsigned)len2; | |
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); | |
} | |
/* ========================================================================= */ | |
uLong ZEXPORT adler32_combine(adler1, adler2, len2) | |
uLong adler1; | |
uLong adler2; | |
z_off_t len2; | |
{ | |
return adler32_combine_(adler1, adler2, len2); | |
} | |
uLong ZEXPORT adler32_combine64(adler1, adler2, len2) | |
uLong adler1; | |
uLong adler2; | |
z_off64_t len2; | |
{ | |
return adler32_combine_(adler1, adler2, len2); | |
} |