1 | /* inffast.c -- fast decoding |
---|
2 | * Copyright (C) 1995-2008 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 | */ |
---|
67 | void inflate_fast(strm, start) |
---|
68 | z_streamp strm; |
---|
69 | unsigned start; /* inflate()'s starting value for strm->avail_out */ |
---|
70 | { |
---|
71 | struct inflate_state FAR *state; |
---|
72 | unsigned char FAR *in; /* local strm->next_in */ |
---|
73 | unsigned char FAR *last; /* while in < last, enough input available */ |
---|
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 */ |
---|