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Comparing liblzf/lzf_c.c (file contents):
Revision 1.36 by root, Fri May 1 00:30:53 2009 UTC vs.
Revision 1.45 by root, Sun Mar 27 23:53:23 2011 UTC

1/* 1/*
2 * Copyright (c) 2000-2008 Marc Alexander Lehmann <schmorp@schmorp.de> 2 * Copyright (c) 2000-2010 Marc Alexander Lehmann <schmorp@schmorp.de>
3 * 3 *
4 * Redistribution and use in source and binary forms, with or without modifica- 4 * Redistribution and use in source and binary forms, with or without modifica-
5 * tion, are permitted provided that the following conditions are met: 5 * tion, are permitted provided that the following conditions are met:
6 * 6 *
7 * 1. Redistributions of source code must retain the above copyright notice, 7 * 1. Redistributions of source code must retain the above copyright notice,
… …
38 38
39#define HSIZE (1 << (HLOG)) 39#define HSIZE (1 << (HLOG))
40 40
41/* 41/*
42 * don't play with this unless you benchmark! 42 * don't play with this unless you benchmark!
43 * decompression is not dependent on the hash function 43 * the data format is not dependent on the hash function.
44 * the hashing function might seem strange, just believe me 44 * the hash function might seem strange, just believe me,
45 * it works ;) 45 * it works ;)
46 */ 46 */
47#ifndef FRST 47#ifndef FRST
48# define FRST(p) (((p[0]) << 8) | p[1]) 48# define FRST(p) (((p[0]) << 8) | p[1])
49# define NEXT(v,p) (((v) << 8) | p[2]) 49# define NEXT(v,p) (((v) << 8) | p[2])
50# if MULTIPLICATION_IS_SLOW
50# if ULTRA_FAST 51# if ULTRA_FAST
51# define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1)) 52# define IDX(h) ((( h >> (3*8 - HLOG)) - h ) & (HSIZE - 1))
52# elif VERY_FAST 53# elif VERY_FAST
53# define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) 54# define IDX(h) ((( h >> (3*8 - HLOG)) - h*5) & (HSIZE - 1))
55# else
56# define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1))
57# endif
54# else 58# else
59/* this one was developed with sesse,
60 * and is very similar to the one in snappy.
61 * it does need a modern enough cpu with a fast multiplication.
62 */
55# define IDX(h) ((((h ^ (h << 5)) >> (3*8 - HLOG)) - h*5) & (HSIZE - 1)) 63# define IDX(h) (((h * 0x1e35a7bdU) >> (32 - HLOG - 8)) & (HSIZE - 1))
56# endif 64# endif
57#endif 65#endif
58/*
59 * IDX works because it is very similar to a multiplicative hash, e.g.
60 * ((h * 57321 >> (3*8 - HLOG)) & (HSIZE - 1))
61 * the latter is also quite fast on newer CPUs, and compresses similarly.
62 *
63 * the next one is also quite good, albeit slow ;)
64 * (int)(cos(h & 0xffffff) * 1e6)
65 */
66 66
67#if 0 67#if 0
68/* original lzv-like hash function, much worse and thus slower */ 68/* original lzv-like hash function, much worse and thus slower */
69# define FRST(p) (p[0] << 5) ^ p[1] 69# define FRST(p) (p[0] << 5) ^ p[1]
70# define NEXT(v,p) ((v) << 5) ^ p[2] 70# define NEXT(v,p) ((v) << 5) ^ p[2]
… …
87#define expect_true(expr) expect ((expr) != 0, 1) 87#define expect_true(expr) expect ((expr) != 0, 1)
88 88
89/* 89/*
90 * compressed format 90 * compressed format
91 * 91 *
92 * 000LLLLL <L+1> ; literal 92 * 000LLLLL <L+1> ; literal, L+1=1..33 octets
93 * LLLooooo oooooooo ; backref L 93 * LLLooooo oooooooo ; backref L+1=1..7 octets, o+1=1..4096 offset
94 * 111ooooo LLLLLLLL oooooooo ; backref L+7 94 * 111ooooo LLLLLLLL oooooooo ; backref L+8 octets, o+1=1..4096 offset
95 * 95 *
96 */ 96 */
97 97
98unsigned int 98unsigned int
99lzf_compress (const void *const in_data, unsigned int in_len, 99lzf_compress (const void *const in_data, unsigned int in_len,
… …
104 ) 104 )
105{ 105{
106#if !LZF_STATE_ARG 106#if !LZF_STATE_ARG
107 LZF_STATE htab; 107 LZF_STATE htab;
108#endif 108#endif
109 const u8 **hslot;
110 const u8 *ip = (const u8 *)in_data; 109 const u8 *ip = (const u8 *)in_data;
111 u8 *op = (u8 *)out_data; 110 u8 *op = (u8 *)out_data;
112 const u8 *in_end = ip + in_len; 111 const u8 *in_end = ip + in_len;
113 u8 *out_end = op + out_len; 112 u8 *out_end = op + out_len;
114 const u8 *ref; 113 const u8 *ref;
… …
131 if (!in_len || !out_len) 130 if (!in_len || !out_len)
132 return 0; 131 return 0;
133 132
134#if INIT_HTAB 133#if INIT_HTAB
135 memset (htab, 0, sizeof (htab)); 134 memset (htab, 0, sizeof (htab));
136# if 0
137 for (hslot = htab; hslot < htab + HSIZE; hslot++)
138 *hslot++ = ip;
139# endif
140#endif 135#endif
141 136
142 lit = 0; op++; /* start run */ 137 lit = 0; op++; /* start run */
143 138
144 hval = FRST (ip); 139 hval = FRST (ip);
145 while (ip < in_end - 2) 140 while (ip < in_end - 2)
146 { 141 {
142 LZF_HSLOT *hslot;
143
147 hval = NEXT (hval, ip); 144 hval = NEXT (hval, ip);
148 hslot = htab + IDX (hval); 145 hslot = htab + IDX (hval);
149 ref = *hslot; *hslot = ip; 146 ref = *hslot + LZF_HSLOT_BIAS; *hslot = ip - LZF_HSLOT_BIAS;
150 147
151 if (1 148 if (1
152#if INIT_HTAB 149#if INIT_HTAB
153 && ref < ip /* the next test will actually take care of this, but this is faster */ 150 && ref < ip /* the next test will actually take care of this, but this is faster */
154#endif 151#endif
155 && (off = ip - ref - 1) < MAX_OFF 152 && (off = ip - ref - 1) < MAX_OFF
156 && ip + 4 < in_end
157 && ref > (u8 *)in_data 153 && ref > (u8 *)in_data
154 && ref[2] == ip[2]
158#if STRICT_ALIGN 155#if STRICT_ALIGN
159 && ref[0] == ip[0] 156 && ((ref[1] << 8) | ref[0]) == ((ip[1] << 8) | ip[0])
160 && ref[1] == ip[1]
161 && ref[2] == ip[2]
162#else 157#else
163 && *(u16 *)ref == *(u16 *)ip 158 && *(u16 *)ref == *(u16 *)ip
164 && ref[2] == ip[2]
165#endif 159#endif
166 ) 160 )
167 { 161 {
168 /* match found at *ref++ */ 162 /* match found at *ref++ */
169 unsigned int len = 2; 163 unsigned int len = 2;
… …
221 *op++ = (off >> 8) + ( 7 << 5); 215 *op++ = (off >> 8) + ( 7 << 5);
222 *op++ = len - 7; 216 *op++ = len - 7;
223 } 217 }
224 218
225 *op++ = off; 219 *op++ = off;
220
226 lit = 0; op++; /* start run */ 221 lit = 0; op++; /* start run */
227 222
228 ip += len + 1; 223 ip += len + 1;
229 224
230 if (expect_false (ip >= in_end - 2)) 225 if (expect_false (ip >= in_end - 2))
… …
236 --ip; 231 --ip;
237# endif 232# endif
238 hval = FRST (ip); 233 hval = FRST (ip);
239 234
240 hval = NEXT (hval, ip); 235 hval = NEXT (hval, ip);
241 htab[IDX (hval)] = ip; 236 htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
242 ip++; 237 ip++;
243 238
244# if VERY_FAST && !ULTRA_FAST 239# if VERY_FAST && !ULTRA_FAST
245 hval = NEXT (hval, ip); 240 hval = NEXT (hval, ip);
246 htab[IDX (hval)] = ip; 241 htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
247 ip++; 242 ip++;
248# endif 243# endif
249#else 244#else
250 ip -= len + 1; 245 ip -= len + 1;
251 246
252 do 247 do
253 { 248 {
254 hval = NEXT (hval, ip); 249 hval = NEXT (hval, ip);
255 htab[IDX (hval)] = ip; 250 htab[IDX (hval)] = ip - LZF_HSLOT_BIAS;
256 ip++; 251 ip++;
257 } 252 }
258 while (len--); 253 while (len--);
259#endif 254#endif
260 } 255 }

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