source: Vago/zlib-1.2.8/inffast.c@ 1050

Last change on this file since 1050 was 1049, checked in by s10k, 8 years ago
File size: 13.1 KB
RevLine 
[1049]1/* inffast.c -- fast decoding
2 * Copyright (C) 1995-2008, 2010, 2013 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6#include "zutil.h"
7#include "inftrees.h"
8#include "inflate.h"
9#include "inffast.h"
10
11#ifndef ASMINF
12
13/* Allow machine dependent optimization for post-increment or pre-increment.
14 Based on testing to date,
15 Pre-increment preferred for:
16 - PowerPC G3 (Adler)
17 - MIPS R5000 (Randers-Pehrson)
18 Post-increment preferred for:
19 - none
20 No measurable difference:
21 - Pentium III (Anderson)
22 - M68060 (Nikl)
23 */
24#ifdef POSTINC
25# define OFF 0
26# define PUP(a) *(a)++
27#else
28# define OFF 1
29# define PUP(a) *++(a)
30#endif
31
32/*
33 Decode literal, length, and distance codes and write out the resulting
34 literal and match bytes until either not enough input or output is
35 available, an end-of-block is encountered, or a data error is encountered.
36 When large enough input and output buffers are supplied to inflate(), for
37 example, a 16K input buffer and a 64K output buffer, more than 95% of the
38 inflate execution time is spent in this routine.
39
40 Entry assumptions:
41
42 state->mode == LEN
43 strm->avail_in >= 6
44 strm->avail_out >= 258
45 start >= strm->avail_out
46 state->bits < 8
47
48 On return, state->mode is one of:
49
50 LEN -- ran out of enough output space or enough available input
51 TYPE -- reached end of block code, inflate() to interpret next block
52 BAD -- error in block data
53
54 Notes:
55
56 - The maximum input bits used by a length/distance pair is 15 bits for the
57 length code, 5 bits for the length extra, 15 bits for the distance code,
58 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
59 Therefore if strm->avail_in >= 6, then there is enough input to avoid
60 checking for available input while decoding.
61
62 - The maximum bytes that a single length/distance pair can output is 258
63 bytes, which is the maximum length that can be coded. inflate_fast()
64 requires strm->avail_out >= 258 for each loop to avoid checking for
65 output space.
66 */
67void ZLIB_INTERNAL inflate_fast(strm, start)
68z_streamp strm;
69unsigned start; /* inflate()'s starting value for strm->avail_out */
70{
71 struct inflate_state FAR *state;
72 z_const unsigned char FAR *in; /* local strm->next_in */
73 z_const unsigned char FAR *last; /* have enough input while in < last */
74 unsigned char FAR *out; /* local strm->next_out */
75 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
76 unsigned char FAR *end; /* while out < end, enough space available */
77#ifdef INFLATE_STRICT
78 unsigned dmax; /* maximum distance from zlib header */
79#endif
80 unsigned wsize; /* window size or zero if not using window */
81 unsigned whave; /* valid bytes in the window */
82 unsigned wnext; /* window write index */
83 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
84 unsigned long hold; /* local strm->hold */
85 unsigned bits; /* local strm->bits */
86 code const FAR *lcode; /* local strm->lencode */
87 code const FAR *dcode; /* local strm->distcode */
88 unsigned lmask; /* mask for first level of length codes */
89 unsigned dmask; /* mask for first level of distance codes */
90 code here; /* retrieved table entry */
91 unsigned op; /* code bits, operation, extra bits, or */
92 /* window position, window bytes to copy */
93 unsigned len; /* match length, unused bytes */
94 unsigned dist; /* match distance */
95 unsigned char FAR *from; /* where to copy match from */
96
97 /* copy state to local variables */
98 state = (struct inflate_state FAR *)strm->state;
99 in = strm->next_in - OFF;
100 last = in + (strm->avail_in - 5);
101 out = strm->next_out - OFF;
102 beg = out - (start - strm->avail_out);
103 end = out + (strm->avail_out - 257);
104#ifdef INFLATE_STRICT
105 dmax = state->dmax;
106#endif
107 wsize = state->wsize;
108 whave = state->whave;
109 wnext = state->wnext;
110 window = state->window;
111 hold = state->hold;
112 bits = state->bits;
113 lcode = state->lencode;
114 dcode = state->distcode;
115 lmask = (1U << state->lenbits) - 1;
116 dmask = (1U << state->distbits) - 1;
117
118 /* decode literals and length/distances until end-of-block or not enough
119 input data or output space */
120 do {
121 if (bits < 15) {
122 hold += (unsigned long)(PUP(in)) << bits;
123 bits += 8;
124 hold += (unsigned long)(PUP(in)) << bits;
125 bits += 8;
126 }
127 here = lcode[hold & lmask];
128 dolen:
129 op = (unsigned)(here.bits);
130 hold >>= op;
131 bits -= op;
132 op = (unsigned)(here.op);
133 if (op == 0) { /* literal */
134 Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
135 "inflate: literal '%c'\n" :
136 "inflate: literal 0x%02x\n", here.val));
137 PUP(out) = (unsigned char)(here.val);
138 }
139 else if (op & 16) { /* length base */
140 len = (unsigned)(here.val);
141 op &= 15; /* number of extra bits */
142 if (op) {
143 if (bits < op) {
144 hold += (unsigned long)(PUP(in)) << bits;
145 bits += 8;
146 }
147 len += (unsigned)hold & ((1U << op) - 1);
148 hold >>= op;
149 bits -= op;
150 }
151 Tracevv((stderr, "inflate: length %u\n", len));
152 if (bits < 15) {
153 hold += (unsigned long)(PUP(in)) << bits;
154 bits += 8;
155 hold += (unsigned long)(PUP(in)) << bits;
156 bits += 8;
157 }
158 here = dcode[hold & dmask];
159 dodist:
160 op = (unsigned)(here.bits);
161 hold >>= op;
162 bits -= op;
163 op = (unsigned)(here.op);
164 if (op & 16) { /* distance base */
165 dist = (unsigned)(here.val);
166 op &= 15; /* number of extra bits */
167 if (bits < op) {
168 hold += (unsigned long)(PUP(in)) << bits;
169 bits += 8;
170 if (bits < op) {
171 hold += (unsigned long)(PUP(in)) << bits;
172 bits += 8;
173 }
174 }
175 dist += (unsigned)hold & ((1U << op) - 1);
176#ifdef INFLATE_STRICT
177 if (dist > dmax) {
178 strm->msg = (char *)"invalid distance too far back";
179 state->mode = BAD;
180 break;
181 }
182#endif
183 hold >>= op;
184 bits -= op;
185 Tracevv((stderr, "inflate: distance %u\n", dist));
186 op = (unsigned)(out - beg); /* max distance in output */
187 if (dist > op) { /* see if copy from window */
188 op = dist - op; /* distance back in window */
189 if (op > whave) {
190 if (state->sane) {
191 strm->msg =
192 (char *)"invalid distance too far back";
193 state->mode = BAD;
194 break;
195 }
196#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
197 if (len <= op - whave) {
198 do {
199 PUP(out) = 0;
200 } while (--len);
201 continue;
202 }
203 len -= op - whave;
204 do {
205 PUP(out) = 0;
206 } while (--op > whave);
207 if (op == 0) {
208 from = out - dist;
209 do {
210 PUP(out) = PUP(from);
211 } while (--len);
212 continue;
213 }
214#endif
215 }
216 from = window - OFF;
217 if (wnext == 0) { /* very common case */
218 from += wsize - op;
219 if (op < len) { /* some from window */
220 len -= op;
221 do {
222 PUP(out) = PUP(from);
223 } while (--op);
224 from = out - dist; /* rest from output */
225 }
226 }
227 else if (wnext < op) { /* wrap around window */
228 from += wsize + wnext - op;
229 op -= wnext;
230 if (op < len) { /* some from end of window */
231 len -= op;
232 do {
233 PUP(out) = PUP(from);
234 } while (--op);
235 from = window - OFF;
236 if (wnext < len) { /* some from start of window */
237 op = wnext;
238 len -= op;
239 do {
240 PUP(out) = PUP(from);
241 } while (--op);
242 from = out - dist; /* rest from output */
243 }
244 }
245 }
246 else { /* contiguous in window */
247 from += wnext - op;
248 if (op < len) { /* some from window */
249 len -= op;
250 do {
251 PUP(out) = PUP(from);
252 } while (--op);
253 from = out - dist; /* rest from output */
254 }
255 }
256 while (len > 2) {
257 PUP(out) = PUP(from);
258 PUP(out) = PUP(from);
259 PUP(out) = PUP(from);
260 len -= 3;
261 }
262 if (len) {
263 PUP(out) = PUP(from);
264 if (len > 1)
265 PUP(out) = PUP(from);
266 }
267 }
268 else {
269 from = out - dist; /* copy direct from output */
270 do { /* minimum length is three */
271 PUP(out) = PUP(from);
272 PUP(out) = PUP(from);
273 PUP(out) = PUP(from);
274 len -= 3;
275 } while (len > 2);
276 if (len) {
277 PUP(out) = PUP(from);
278 if (len > 1)
279 PUP(out) = PUP(from);
280 }
281 }
282 }
283 else if ((op & 64) == 0) { /* 2nd level distance code */
284 here = dcode[here.val + (hold & ((1U << op) - 1))];
285 goto dodist;
286 }
287 else {
288 strm->msg = (char *)"invalid distance code";
289 state->mode = BAD;
290 break;
291 }
292 }
293 else if ((op & 64) == 0) { /* 2nd level length code */
294 here = lcode[here.val + (hold & ((1U << op) - 1))];
295 goto dolen;
296 }
297 else if (op & 32) { /* end-of-block */
298 Tracevv((stderr, "inflate: end of block\n"));
299 state->mode = TYPE;
300 break;
301 }
302 else {
303 strm->msg = (char *)"invalid literal/length code";
304 state->mode = BAD;
305 break;
306 }
307 } while (in < last && out < end);
308
309 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
310 len = bits >> 3;
311 in -= len;
312 bits -= len << 3;
313 hold &= (1U << bits) - 1;
314
315 /* update state and return */
316 strm->next_in = in + OFF;
317 strm->next_out = out + OFF;
318 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
319 strm->avail_out = (unsigned)(out < end ?
320 257 + (end - out) : 257 - (out - end));
321 state->hold = hold;
322 state->bits = bits;
323 return;
324}
325
326/*
327 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
328 - Using bit fields for code structure
329 - Different op definition to avoid & for extra bits (do & for table bits)
330 - Three separate decoding do-loops for direct, window, and wnext == 0
331 - Special case for distance > 1 copies to do overlapped load and store copy
332 - Explicit branch predictions (based on measured branch probabilities)
333 - Deferring match copy and interspersed it with decoding subsequent codes
334 - Swapping literal/length else
335 - Swapping window/direct else
336 - Larger unrolled copy loops (three is about right)
337 - Moving len -= 3 statement into middle of loop
338 */
339
340#endif /* !ASMINF */
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