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