1 : /* inffast.c -- fast decoding
2 : * Copyright (C) 1995-2008, 2010 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 1671 : void ZLIB_INTERNAL 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 1671 : state = (struct inflate_state FAR *)strm->state;
99 1671 : in = strm->next_in - OFF;
100 1671 : last = in + (strm->avail_in - 5);
101 1671 : out = strm->next_out - OFF;
102 1671 : beg = out - (start - strm->avail_out);
103 1671 : end = out + (strm->avail_out - 257);
104 : #ifdef INFLATE_STRICT
105 : dmax = state->dmax;
106 : #endif
107 1671 : wsize = state->wsize;
108 1671 : whave = state->whave;
109 1671 : wnext = state->wnext;
110 1671 : window = state->window;
111 1671 : hold = state->hold;
112 1671 : bits = state->bits;
113 1671 : lcode = state->lencode;
114 1671 : dcode = state->distcode;
115 1671 : lmask = (1U << state->lenbits) - 1;
116 1671 : 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 300213 : if (bits < 15) {
122 114635 : hold += (unsigned long)(PUP(in)) << bits;
123 114635 : bits += 8;
124 114635 : hold += (unsigned long)(PUP(in)) << bits;
125 114635 : bits += 8;
126 : }
127 300213 : here = lcode[hold & lmask];
128 : dolen:
129 300243 : op = (unsigned)(here.bits);
130 300243 : hold >>= op;
131 300243 : bits -= op;
132 300243 : op = (unsigned)(here.op);
133 300243 : 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 256332 : PUP(out) = (unsigned char)(here.val);
138 : }
139 43911 : else if (op & 16) { /* length base */
140 43879 : len = (unsigned)(here.val);
141 43879 : op &= 15; /* number of extra bits */
142 43879 : if (op) {
143 7922 : if (bits < op) {
144 0 : hold += (unsigned long)(PUP(in)) << bits;
145 0 : bits += 8;
146 : }
147 7922 : len += (unsigned)hold & ((1U << op) - 1);
148 7922 : hold >>= op;
149 7922 : bits -= op;
150 : }
151 : Tracevv((stderr, "inflate: length %u\n", len));
152 43879 : if (bits < 15) {
153 17296 : hold += (unsigned long)(PUP(in)) << bits;
154 17296 : bits += 8;
155 17296 : hold += (unsigned long)(PUP(in)) << bits;
156 17296 : bits += 8;
157 : }
158 43879 : here = dcode[hold & dmask];
159 : dodist:
160 43910 : op = (unsigned)(here.bits);
161 43910 : hold >>= op;
162 43910 : bits -= op;
163 43910 : op = (unsigned)(here.op);
164 43910 : if (op & 16) { /* distance base */
165 43879 : dist = (unsigned)(here.val);
166 43879 : op &= 15; /* number of extra bits */
167 43879 : if (bits < op) {
168 1 : hold += (unsigned long)(PUP(in)) << bits;
169 1 : bits += 8;
170 1 : if (bits < op) {
171 0 : hold += (unsigned long)(PUP(in)) << bits;
172 0 : bits += 8;
173 : }
174 : }
175 43879 : 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 43879 : hold >>= op;
184 43879 : bits -= op;
185 : Tracevv((stderr, "inflate: distance %u\n", dist));
186 43879 : op = (unsigned)(out - beg); /* max distance in output */
187 43879 : if (dist > op) { /* see if copy from window */
188 57 : op = dist - op; /* distance back in window */
189 57 : if (op > whave) {
190 0 : if (state->sane) {
191 0 : strm->msg =
192 : (char *)"invalid distance too far back";
193 0 : state->mode = BAD;
194 0 : 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 57 : from = window - OFF;
217 57 : if (wnext == 0) { /* very common case */
218 0 : from += wsize - op;
219 0 : if (op < len) { /* some from window */
220 0 : len -= op;
221 : do {
222 0 : PUP(out) = PUP(from);
223 0 : } while (--op);
224 0 : from = out - dist; /* rest from output */
225 : }
226 : }
227 57 : else if (wnext < op) { /* wrap around window */
228 0 : from += wsize + wnext - op;
229 0 : op -= wnext;
230 0 : if (op < len) { /* some from end of window */
231 0 : len -= op;
232 : do {
233 0 : PUP(out) = PUP(from);
234 0 : } while (--op);
235 0 : from = window - OFF;
236 0 : if (wnext < len) { /* some from start of window */
237 0 : op = wnext;
238 0 : len -= op;
239 : do {
240 0 : PUP(out) = PUP(from);
241 0 : } while (--op);
242 0 : from = out - dist; /* rest from output */
243 : }
244 : }
245 : }
246 : else { /* contiguous in window */
247 57 : from += wnext - op;
248 57 : if (op < len) { /* some from window */
249 0 : len -= op;
250 : do {
251 0 : PUP(out) = PUP(from);
252 0 : } while (--op);
253 0 : from = out - dist; /* rest from output */
254 : }
255 : }
256 426 : while (len > 2) {
257 312 : PUP(out) = PUP(from);
258 312 : PUP(out) = PUP(from);
259 312 : PUP(out) = PUP(from);
260 312 : len -= 3;
261 : }
262 57 : if (len) {
263 31 : PUP(out) = PUP(from);
264 31 : if (len > 1)
265 8 : PUP(out) = PUP(from);
266 : }
267 : }
268 : else {
269 43822 : from = out - dist; /* copy direct from output */
270 : do { /* minimum length is three */
271 108377 : PUP(out) = PUP(from);
272 108377 : PUP(out) = PUP(from);
273 108377 : PUP(out) = PUP(from);
274 108377 : len -= 3;
275 108377 : } while (len > 2);
276 43822 : if (len) {
277 26545 : PUP(out) = PUP(from);
278 26545 : if (len > 1)
279 13886 : PUP(out) = PUP(from);
280 : }
281 : }
282 : }
283 31 : else if ((op & 64) == 0) { /* 2nd level distance code */
284 31 : here = dcode[here.val + (hold & ((1U << op) - 1))];
285 31 : goto dodist;
286 : }
287 : else {
288 0 : strm->msg = (char *)"invalid distance code";
289 0 : state->mode = BAD;
290 0 : break;
291 : }
292 : }
293 32 : else if ((op & 64) == 0) { /* 2nd level length code */
294 30 : here = lcode[here.val + (hold & ((1U << op) - 1))];
295 30 : goto dolen;
296 : }
297 2 : else if (op & 32) { /* end-of-block */
298 : Tracevv((stderr, "inflate: end of block\n"));
299 2 : state->mode = TYPE;
300 2 : break;
301 : }
302 : else {
303 0 : strm->msg = (char *)"invalid literal/length code";
304 0 : state->mode = BAD;
305 0 : break;
306 : }
307 300211 : } while (in < last && out < end);
308 :
309 : /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
310 1671 : len = bits >> 3;
311 1671 : in -= len;
312 1671 : bits -= len << 3;
313 1671 : hold &= (1U << bits) - 1;
314 :
315 : /* update state and return */
316 1671 : strm->next_in = in + OFF;
317 1671 : strm->next_out = out + OFF;
318 1671 : strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
319 3342 : strm->avail_out = (unsigned)(out < end ?
320 1671 : 257 + (end - out) : 257 - (out - end));
321 1671 : state->hold = hold;
322 1671 : 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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