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/* 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 | ||
*/ | ||
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/* @(#) $Id$ */ | ||
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#include "zutil.h" | ||
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#define local static | ||
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local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); | ||
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#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 */ | ||
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#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); | ||
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/* 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 | ||
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#if defined(ADLER32_SIMD_NEON) || defined (ADLER32_SIMD_SSSE3) | ||
#include "adler32_simd.h" | ||
#endif | ||
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/* ========================================================================= */ | ||
uLong ZEXPORT adler32(adler, buf, len) | ||
uLong adler; | ||
const Bytef *buf; | ||
uInt len; | ||
{ | ||
unsigned long sum2; | ||
unsigned n; | ||
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#if defined(ADLER32_SIMD_NEON) || defined(ADLER32_SIMD_SSSE3) | ||
if (buf && len >= 64) | ||
return adler32_simd_(adler, buf, len); | ||
#endif | ||
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/* split Adler-32 into component sums */ | ||
sum2 = (adler >> 16) & 0xffff; | ||
adler &= 0xffff; | ||
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/* 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); | ||
} | ||
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/* initial Adler-32 value (deferred check for len == 1 speed) */ | ||
if (buf == Z_NULL) | ||
return 1L; | ||
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/* 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); | ||
} | ||
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/* 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); | ||
} | ||
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/* 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); | ||
} | ||
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/* return recombined sums */ | ||
return adler | (sum2 << 16); | ||
} | ||
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/* ========================================================================= */ | ||
local uLong adler32_combine_(adler1, adler2, len2) | ||
uLong adler1; | ||
uLong adler2; | ||
z_off64_t len2; | ||
{ | ||
unsigned long sum1; | ||
unsigned long sum2; | ||
unsigned rem; | ||
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/* for negative len, return invalid adler32 as a clue for debugging */ | ||
if (len2 < 0) | ||
return 0xffffffffUL; | ||
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/* 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); | ||
} | ||
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/* ========================================================================= */ | ||
uLong ZEXPORT adler32_combine(adler1, adler2, len2) | ||
uLong adler1; | ||
uLong adler2; | ||
z_off_t len2; | ||
{ | ||
return adler32_combine_(adler1, adler2, len2); | ||
} | ||
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uLong ZEXPORT adler32_combine64(adler1, adler2, len2) | ||
uLong adler1; | ||
uLong adler2; | ||
z_off64_t len2; | ||
{ | ||
return adler32_combine_(adler1, adler2, len2); | ||
} |
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