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redis_study/src/lzf_c.c
zeekling 2e3acd7713 创建redis源码学习
2020-09-05 12:01:22 +08:00

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/*
* Copyright (c) 2000-2010 Marc Alexander Lehmann <schmorp@schmorp.de>
*
* Redistribution and use in source and binary forms, with or without modifica-
* tion, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
* CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
* CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
* ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Alternatively, the contents of this file may be used under the terms of
* the GNU General Public License ("GPL") version 2 or any later version,
* in which case the provisions of the GPL are applicable instead of
* the above. If you wish to allow the use of your version of this file
* only under the terms of the GPL and not to allow others to use your
* version of this file under the BSD license, indicate your decision
* by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL. If you do not delete the
* provisions above, a recipient may use your version of this file under
* either the BSD or the GPL.
*/
#include "lzfP.h"
#define HSIZE (1 << (HLOG))
/*
* don't play with this unless you benchmark!
* the data format is not dependent on the hash function.
* the hash function might seem strange, just believe me,
* it works ;)
*/
#ifndef FRST
# define FRST(p) (((p[0]) << 8) | p[1])
# define NEXT(v,p) (((v) << 8) | p[2])
# if ULTRA_FAST
# define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1))
# elif VERY_FAST
# define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1))
# else
# define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1))
# endif
#endif
/*
* IDX works because it is very similar to a multiplicative hash, e.g.
* ((h * 57321 >> (3*8 - HLOG)) & (HSIZE - 1))
* the latter is also quite fast on newer CPUs, and compresses similarly.
*
* the next one is also quite good, albeit slow ;)
* (int)(cos(h & 0xffffff) * 1e6)
*/
#if 0
/* original lzv-like hash function, much worse and thus slower */
# define FRST(p) (p[0] << 5) ^ p[1]
# define NEXT(v,p) ((v) << 5) ^ p[2]
# define IDX(h) ((h) & (HSIZE - 1))
#endif
#define MAX_LIT (1 << 5)
#define MAX_OFF (1 << 13)
#define MAX_REF ((1 << 8) + (1 << 3))
#if __GNUC__ >= 3
# define expect(expr,value) __builtin_expect ((expr),(value))
# define inline inline
#else
# define expect(expr,value) (expr)
# define inline static
#endif
#define expect_false(expr) expect ((expr) != 0, 0)
#define expect_true(expr) expect ((expr) != 0, 1)
/*
* compressed format
*
* 000LLLLL <L+1> ; literal, L+1=1..33 octets
* LLLooooo oooooooo ; backref L+1=1..7 octets, o+1=1..4096 offset
* 111ooooo LLLLLLLL oooooooo ; backref L+8 octets, o+1=1..4096 offset
*
*/
unsigned int
lzf_compress (const void *const in_data, unsigned int in_len,
void *out_data, unsigned int out_len
#if LZF_STATE_ARG
, LZF_STATE htab
#endif
)
{
#if !LZF_STATE_ARG
LZF_STATE htab;
#endif
const u8 *ip = (const u8 *)in_data;
u8 *op = (u8 *)out_data;
const u8 *in_end = ip + in_len;
u8 *out_end = op + out_len;
const u8 *ref;
/* off requires a type wide enough to hold a general pointer difference.
* ISO C doesn't have that (size_t might not be enough and ptrdiff_t only
* works for differences within a single object). We also assume that no
* no bit pattern traps. Since the only platform that is both non-POSIX
* and fails to support both assumptions is windows 64 bit, we make a
* special workaround for it.
*/
#if defined (WIN32) && defined (_M_X64)
unsigned _int64 off; /* workaround for missing POSIX compliance */
#else
unsigned long off;
#endif
unsigned int hval;
int lit;
if (!in_len || !out_len)
return 0;
#if INIT_HTAB
memset (htab, 0, sizeof (htab));
#endif
lit = 0; op++; /* start run */
hval = FRST (ip);
while (ip < in_end - 2)
{
LZF_HSLOT *hslot;
hval = NEXT (hval, ip);
hslot = htab + IDX (hval);
ref = *hslot + LZF_HSLOT_BIAS; *hslot = ip - LZF_HSLOT_BIAS;
if (1
#if INIT_HTAB
&& ref < ip /* the next test will actually take care of this, but this is faster */
#endif
&& (off = ip - ref - 1) < MAX_OFF
&& ref > (u8 *)in_data
&& ref[2] == ip[2]
#if STRICT_ALIGN
&& ((ref[1] << 8) | ref[0]) == ((ip[1] << 8) | ip[0])
#else
&& *(u16 *)ref == *(u16 *)ip
#endif
)
{
/* match found at *ref++ */
unsigned int len = 2;
unsigned int maxlen = in_end - ip - len;
maxlen = maxlen > MAX_REF ? MAX_REF : maxlen;
if (expect_false (op + 3 + 1 >= out_end)) /* first a faster conservative test */
if (op - !lit + 3 + 1 >= out_end) /* second the exact but rare test */
return 0;
op [- lit - 1] = lit - 1; /* stop run */
op -= !lit; /* undo run if length is zero */
for (;;)
{
if (expect_true (maxlen > 16))
{
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
len++; if (ref [len] != ip [len]) break;
}
do
len++;
while (len < maxlen && ref[len] == ip[len]);
break;
}
len -= 2; /* len is now #octets - 1 */
ip++;
if (len < 7)
{
*op++ = (off >> 8) + (len << 5);
}
else
{
*op++ = (off >> 8) + ( 7 << 5);
*op++ = len - 7;
}
*op++ = off;
lit = 0; op++; /* start run */
ip += len + 1;
if (expect_false (ip >= in_end - 2))
break;
#if ULTRA_FAST || VERY_FAST
--ip;
# if VERY_FAST && !ULTRA_FAST
--ip;
# endif
hval = FRST (ip);
hval = NEXT (hval, ip);
htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
ip++;
# if VERY_FAST && !ULTRA_FAST
hval = NEXT (hval, ip);
htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
ip++;
# endif
#else
ip -= len + 1;
do
{
hval = NEXT (hval, ip);
htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
ip++;
}
while (len--);
#endif
}
else
{
/* one more literal byte we must copy */
if (expect_false (op >= out_end))
return 0;
lit++; *op++ = *ip++;
if (expect_false (lit == MAX_LIT))
{
op [- lit - 1] = lit - 1; /* stop run */
lit = 0; op++; /* start run */
}
}
}
if (op + 3 > out_end) /* at most 3 bytes can be missing here */
return 0;
while (ip < in_end)
{
lit++; *op++ = *ip++;
if (expect_false (lit == MAX_LIT))
{
op [- lit - 1] = lit - 1; /* stop run */
lit = 0; op++; /* start run */
}
}
op [- lit - 1] = lit - 1; /* end run */
op -= !lit; /* undo run if length is zero */
return op - (u8 *)out_data;
}
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