1 /* inffast.c -- fast decoding
2 * Copyright (C) 1995-2017 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 #ifdef ASMINF
12 # pragma message("Assembler code may have bugs -- use at your own risk")
13 #else
14
15 /*
16 Decode literal, length, and distance codes and write out the resulting
17 literal and match bytes until either not enough input or output is
18 available, an end-of-block is encountered, or a data error is encountered.
19 When large enough input and output buffers are supplied to inflate(), for
20 example, a 16K input buffer and a 64K output buffer, more than 95% of the
21 inflate execution time is spent in this routine.
22
23 Entry assumptions:
24
25 state->mode == LEN
26 strm->avail_in >= 6
27 strm->avail_out >= 258
28 start >= strm->avail_out
29 state->bits < 8
30
31 On return, state->mode is one of:
32
33 LEN -- ran out of enough output space or enough available input
34 TYPE -- reached end of block code, inflate() to interpret next block
35 BAD -- error in block data
36
37 Notes:
38
39 - The maximum input bits used by a length/distance pair is 15 bits for the
40 length code, 5 bits for the length extra, 15 bits for the distance code,
41 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
42 Therefore if strm->avail_in >= 6, then there is enough input to avoid
43 checking for available input while decoding.
44
45 - The maximum bytes that a single length/distance pair can output is 258
46 bytes, which is the maximum length that can be coded. inflate_fast()
47 requires strm->avail_out >= 258 for each loop to avoid checking for
48 output space.
49 */
inflate_fast(z_streamp strm,unsigned start)50 void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
51 struct inflate_state FAR *state;
52 z_const unsigned char FAR *in; /* local strm->next_in */
53 z_const unsigned char FAR *last; /* have enough input while in < last */
54 unsigned char FAR *out; /* local strm->next_out */
55 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
56 unsigned char FAR *end; /* while out < end, enough space available */
57 #ifdef INFLATE_STRICT
58 unsigned dmax; /* maximum distance from zlib header */
59 #endif
60 unsigned wsize; /* window size or zero if not using window */
61 unsigned whave; /* valid bytes in the window */
62 unsigned wnext; /* window write index */
63 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
64 unsigned long hold; /* local strm->hold */
65 unsigned bits; /* local strm->bits */
66 code const FAR *lcode; /* local strm->lencode */
67 code const FAR *dcode; /* local strm->distcode */
68 unsigned lmask; /* mask for first level of length codes */
69 unsigned dmask; /* mask for first level of distance codes */
70 code const *here; /* retrieved table entry */
71 unsigned op; /* code bits, operation, extra bits, or */
72 /* window position, window bytes to copy */
73 unsigned len; /* match length, unused bytes */
74 unsigned dist; /* match distance */
75 unsigned char FAR *from; /* where to copy match from */
76
77 /* copy state to local variables */
78 state = (struct inflate_state FAR *)strm->state;
79 in = strm->next_in;
80 last = in + (strm->avail_in - 5);
81 out = strm->next_out;
82 beg = out - (start - strm->avail_out);
83 end = out + (strm->avail_out - 257);
84 #ifdef INFLATE_STRICT
85 dmax = state->dmax;
86 #endif
87 wsize = state->wsize;
88 whave = state->whave;
89 wnext = state->wnext;
90 window = state->window;
91 hold = state->hold;
92 bits = state->bits;
93 lcode = state->lencode;
94 dcode = state->distcode;
95 lmask = (1U << state->lenbits) - 1;
96 dmask = (1U << state->distbits) - 1;
97
98 /* decode literals and length/distances until end-of-block or not enough
99 input data or output space */
100 do {
101 if (bits < 15) {
102 hold += (unsigned long)(*in++) << bits;
103 bits += 8;
104 hold += (unsigned long)(*in++) << bits;
105 bits += 8;
106 }
107 here = lcode + (hold & lmask);
108 dolen:
109 op = (unsigned)(here->bits);
110 hold >>= op;
111 bits -= op;
112 op = (unsigned)(here->op);
113 if (op == 0) { /* literal */
114 Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ?
115 "inflate: literal '%c'\n" :
116 "inflate: literal 0x%02x\n", here->val));
117 *out++ = (unsigned char)(here->val);
118 }
119 else if (op & 16) { /* length base */
120 len = (unsigned)(here->val);
121 op &= 15; /* number of extra bits */
122 if (op) {
123 if (bits < op) {
124 hold += (unsigned long)(*in++) << bits;
125 bits += 8;
126 }
127 len += (unsigned)hold & ((1U << op) - 1);
128 hold >>= op;
129 bits -= op;
130 }
131 Tracevv((stderr, "inflate: length %u\n", len));
132 if (bits < 15) {
133 hold += (unsigned long)(*in++) << bits;
134 bits += 8;
135 hold += (unsigned long)(*in++) << bits;
136 bits += 8;
137 }
138 here = dcode + (hold & dmask);
139 dodist:
140 op = (unsigned)(here->bits);
141 hold >>= op;
142 bits -= op;
143 op = (unsigned)(here->op);
144 if (op & 16) { /* distance base */
145 dist = (unsigned)(here->val);
146 op &= 15; /* number of extra bits */
147 if (bits < op) {
148 hold += (unsigned long)(*in++) << bits;
149 bits += 8;
150 if (bits < op) {
151 hold += (unsigned long)(*in++) << bits;
152 bits += 8;
153 }
154 }
155 dist += (unsigned)hold & ((1U << op) - 1);
156 #ifdef INFLATE_STRICT
157 if (dist > dmax) {
158 strm->msg = (z_const char *)"invalid distance too far back";
159 state->mode = BAD;
160 break;
161 }
162 #endif
163 hold >>= op;
164 bits -= op;
165 Tracevv((stderr, "inflate: distance %u\n", dist));
166 op = (unsigned)(out - beg); /* max distance in output */
167 if (dist > op) { /* see if copy from window */
168 op = dist - op; /* distance back in window */
169 if (op > whave) {
170 if (state->sane) {
171 #ifdef SMALL
172 strm->msg = (z_const char *)"error";
173 #else
174 strm->msg =
175 (z_const char *)"invalid distance too far back";
176 #endif
177 state->mode = BAD;
178 break;
179 }
180 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
181 if (len <= op - whave) {
182 do {
183 *out++ = 0;
184 } while (--len);
185 continue;
186 }
187 len -= op - whave;
188 do {
189 *out++ = 0;
190 } while (--op > whave);
191 if (op == 0) {
192 from = out - dist;
193 do {
194 *out++ = *from++;
195 } while (--len);
196 continue;
197 }
198 #endif
199 }
200 from = window;
201 if (wnext == 0) { /* very common case */
202 from += wsize - op;
203 if (op < len) { /* some from window */
204 len -= op;
205 do {
206 *out++ = *from++;
207 } while (--op);
208 from = out - dist; /* rest from output */
209 }
210 }
211 else if (wnext < op) { /* wrap around window */
212 from += wsize + wnext - op;
213 op -= wnext;
214 if (op < len) { /* some from end of window */
215 len -= op;
216 do {
217 *out++ = *from++;
218 } while (--op);
219 from = window;
220 if (wnext < len) { /* some from start of window */
221 op = wnext;
222 len -= op;
223 do {
224 *out++ = *from++;
225 } while (--op);
226 from = out - dist; /* rest from output */
227 }
228 }
229 }
230 else { /* contiguous in window */
231 from += wnext - op;
232 if (op < len) { /* some from window */
233 len -= op;
234 do {
235 *out++ = *from++;
236 } while (--op);
237 from = out - dist; /* rest from output */
238 }
239 }
240 while (len > 2) {
241 *out++ = *from++;
242 *out++ = *from++;
243 *out++ = *from++;
244 len -= 3;
245 }
246 if (len) {
247 *out++ = *from++;
248 if (len > 1)
249 *out++ = *from++;
250 }
251 }
252 else {
253 from = out - dist; /* copy direct from output */
254 do { /* minimum length is three */
255 *out++ = *from++;
256 *out++ = *from++;
257 *out++ = *from++;
258 len -= 3;
259 } while (len > 2);
260 if (len) {
261 *out++ = *from++;
262 if (len > 1)
263 *out++ = *from++;
264 }
265 }
266 }
267 else if ((op & 64) == 0) { /* 2nd level distance code */
268 here = dcode + here->val + (hold & ((1U << op) - 1));
269 goto dodist;
270 }
271 else {
272 #ifdef SMALL
273 strm->msg = (z_const char *)"error";
274 #else
275 strm->msg = (z_const char *)"invalid distance code";
276 #endif
277 state->mode = BAD;
278 break;
279 }
280 }
281 else if ((op & 64) == 0) { /* 2nd level length code */
282 here = lcode + here->val + (hold & ((1U << op) - 1));
283 goto dolen;
284 }
285 else if (op & 32) { /* end-of-block */
286 Tracevv((stderr, "inflate: end of block\n"));
287 state->mode = TYPE;
288 break;
289 }
290 else {
291 #ifdef SMALL
292 strm->msg = (z_const char *)"error";
293 #else
294 strm->msg = (z_const char *)"invalid literal/length code";
295 #endif
296 state->mode = BAD;
297 break;
298 }
299 } while (in < last && out < end);
300
301 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
302 len = bits >> 3;
303 in -= len;
304 bits -= len << 3;
305 hold &= (1U << bits) - 1;
306
307 /* update state and return */
308 strm->next_in = in;
309 strm->next_out = out;
310 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
311 strm->avail_out = (unsigned)(out < end ?
312 257 + (end - out) : 257 - (out - end));
313 state->hold = hold;
314 state->bits = bits;
315 return;
316 }
317
318 /*
319 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
320 - Using bit fields for code structure
321 - Different op definition to avoid & for extra bits (do & for table bits)
322 - Three separate decoding do-loops for direct, window, and wnext == 0
323 - Special case for distance > 1 copies to do overlapped load and store copy
324 - Explicit branch predictions (based on measured branch probabilities)
325 - Deferring match copy and interspersed it with decoding subsequent codes
326 - Swapping literal/length else
327 - Swapping window/direct else
328 - Larger unrolled copy loops (three is about right)
329 - Moving len -= 3 statement into middle of loop
330 */
331
332 #endif /* !ASMINF */
333