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