1 // SPDX-License-Identifier: Zlib
2 /* inffast.c -- fast decoding
3 * Copyright (C) 1995-2017 Mark Adler
4 * For conditions of distribution and use, see copyright notice in zlib.h
5 */
6
7 #include "zutil.h"
8 #include "inftrees.h"
9 #include "inflate.h"
10 #include "inffast.h"
11
12 #ifdef ASMINF
13 # pragma message("Assembler code may have bugs -- use at your own risk")
14 #else
15
16 /*
17 Decode literal, length, and distance codes and write out the resulting
18 literal and match bytes until either not enough input or output is
19 available, an end-of-block is encountered, or a data error is encountered.
20 When large enough input and output buffers are supplied to inflate(), for
21 example, a 16K input buffer and a 64K output buffer, more than 95% of the
22 inflate execution time is spent in this routine.
23
24 Entry assumptions:
25
26 state->mode == LEN
27 strm->avail_in >= 6
28 strm->avail_out >= 258
29 start >= strm->avail_out
30 state->bits < 8
31
32 On return, state->mode is one of:
33
34 LEN -- ran out of enough output space or enough available input
35 TYPE -- reached end of block code, inflate() to interpret next block
36 BAD -- error in block data
37
38 Notes:
39
40 - The maximum input bits used by a length/distance pair is 15 bits for the
41 length code, 5 bits for the length extra, 15 bits for the distance code,
42 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
43 Therefore if strm->avail_in >= 6, then there is enough input to avoid
44 checking for available input while decoding.
45
46 - The maximum bytes that a single length/distance pair can output is 258
47 bytes, which is the maximum length that can be coded. inflate_fast()
48 requires strm->avail_out >= 258 for each loop to avoid checking for
49 output space.
50 */
inflate_fast(strm,start)51 void ZLIB_INTERNAL inflate_fast(strm, start)
52 z_streamp strm;
53 unsigned start; /* inflate()'s starting value for strm->avail_out */
54 {
55 struct inflate_state FAR *state;
56 z_const unsigned char FAR *in; /* local strm->next_in */
57 z_const unsigned char FAR *last; /* have enough input while in < last */
58 unsigned char FAR *out; /* local strm->next_out */
59 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
60 unsigned char FAR *end; /* while out < end, enough space available */
61 #ifdef INFLATE_STRICT
62 unsigned dmax; /* maximum distance from zlib header */
63 #endif
64 unsigned wsize; /* window size or zero if not using window */
65 unsigned whave; /* valid bytes in the window */
66 unsigned wnext; /* window write index */
67 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
68 unsigned long hold; /* local strm->hold */
69 unsigned bits; /* local strm->bits */
70 code const FAR *lcode; /* local strm->lencode */
71 code const FAR *dcode; /* local strm->distcode */
72 unsigned lmask; /* mask for first level of length codes */
73 unsigned dmask; /* mask for first level of distance codes */
74 code here; /* retrieved table entry */
75 unsigned op; /* code bits, operation, extra bits, or */
76 /* window position, window bytes to copy */
77 unsigned len; /* match length, unused bytes */
78 unsigned dist; /* match distance */
79 unsigned char FAR *from; /* where to copy match from */
80
81 /* copy state to local variables */
82 state = (struct inflate_state FAR *)strm->state;
83 in = strm->next_in;
84 last = in + (strm->avail_in - 5);
85 out = strm->next_out;
86 beg = out - (start - strm->avail_out);
87 end = out + (strm->avail_out - 257);
88 #ifdef INFLATE_STRICT
89 dmax = state->dmax;
90 #endif
91 wsize = state->wsize;
92 whave = state->whave;
93 wnext = state->wnext;
94 window = state->window;
95 hold = state->hold;
96 bits = state->bits;
97 lcode = state->lencode;
98 dcode = state->distcode;
99 lmask = (1U << state->lenbits) - 1;
100 dmask = (1U << state->distbits) - 1;
101
102 /* decode literals and length/distances until end-of-block or not enough
103 input data or output space */
104 do {
105 if (bits < 15) {
106 hold += (unsigned long)(*in++) << bits;
107 bits += 8;
108 hold += (unsigned long)(*in++) << bits;
109 bits += 8;
110 }
111 here = lcode[hold & lmask];
112 dolen:
113 op = (unsigned)(here.bits);
114 hold >>= op;
115 bits -= op;
116 op = (unsigned)(here.op);
117 if (op == 0) { /* literal */
118 Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
119 "inflate: literal '%c'\n" :
120 "inflate: literal 0x%02x\n", here.val));
121 *out++ = (unsigned char)(here.val);
122 }
123 else if (op & 16) { /* length base */
124 len = (unsigned)(here.val);
125 op &= 15; /* number of extra bits */
126 if (op) {
127 if (bits < op) {
128 hold += (unsigned long)(*in++) << bits;
129 bits += 8;
130 }
131 len += (unsigned)hold & ((1U << op) - 1);
132 hold >>= op;
133 bits -= op;
134 }
135 Tracevv((stderr, "inflate: length %u\n", len));
136 if (bits < 15) {
137 hold += (unsigned long)(*in++) << bits;
138 bits += 8;
139 hold += (unsigned long)(*in++) << bits;
140 bits += 8;
141 }
142 here = dcode[hold & dmask];
143 dodist:
144 op = (unsigned)(here.bits);
145 hold >>= op;
146 bits -= op;
147 op = (unsigned)(here.op);
148 if (op & 16) { /* distance base */
149 dist = (unsigned)(here.val);
150 op &= 15; /* number of extra bits */
151 if (bits < op) {
152 hold += (unsigned long)(*in++) << bits;
153 bits += 8;
154 if (bits < op) {
155 hold += (unsigned long)(*in++) << bits;
156 bits += 8;
157 }
158 }
159 dist += (unsigned)hold & ((1U << op) - 1);
160 #ifdef INFLATE_STRICT
161 if (dist > dmax) {
162 strm->msg = (char *)"invalid distance too far back";
163 state->mode = BAD;
164 break;
165 }
166 #endif
167 hold >>= op;
168 bits -= op;
169 Tracevv((stderr, "inflate: distance %u\n", dist));
170 op = (unsigned)(out - beg); /* max distance in output */
171 if (dist > op) { /* see if copy from window */
172 op = dist - op; /* distance back in window */
173 if (op > whave) {
174 if (state->sane) {
175 strm->msg =
176 (char *)"invalid distance too far back";
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 strm->msg = (char *)"invalid distance code";
273 state->mode = BAD;
274 break;
275 }
276 }
277 else if ((op & 64) == 0) { /* 2nd level length code */
278 here = lcode[here.val + (hold & ((1U << op) - 1))];
279 goto dolen;
280 }
281 else if (op & 32) { /* end-of-block */
282 Tracevv((stderr, "inflate: end of block\n"));
283 state->mode = TYPE;
284 break;
285 }
286 else {
287 strm->msg = (char *)"invalid literal/length code";
288 state->mode = BAD;
289 break;
290 }
291 } while (in < last && out < end);
292
293 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
294 len = bits >> 3;
295 in -= len;
296 bits -= len << 3;
297 hold &= (1U << bits) - 1;
298
299 /* update state and return */
300 strm->next_in = in;
301 strm->next_out = out;
302 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
303 strm->avail_out = (unsigned)(out < end ?
304 257 + (end - out) : 257 - (out - end));
305 state->hold = hold;
306 state->bits = bits;
307 return;
308 }
309
310 /*
311 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
312 - Using bit fields for code structure
313 - Different op definition to avoid & for extra bits (do & for table bits)
314 - Three separate decoding do-loops for direct, window, and wnext == 0
315 - Special case for distance > 1 copies to do overlapped load and store copy
316 - Explicit branch predictions (based on measured branch probabilities)
317 - Deferring match copy and interspersed it with decoding subsequent codes
318 - Swapping literal/length else
319 - Swapping window/direct else
320 - Larger unrolled copy loops (three is about right)
321 - Moving len -= 3 statement into middle of loop
322 */
323
324 #endif /* !ASMINF */
325