1 /*
2 * Copyright (c) 2008-2016, 2020 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
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25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28 /* inffast.c -- fast decoding
29 * Copyright (C) 1995-2004 Mark Adler
30 * For conditions of distribution and use, see copyright notice in zlib.h
31 */
32
33
34 #include "zutil.h"
35 #include "inftrees.h"
36 #include "inflate.h"
37 #include "inffast.h"
38
39 #ifndef ASMINF
40
41 /*
42 Decode literal, length, and distance codes and write out the resulting
43 literal and match bytes until either not enough input or output is
44 available, an end-of-block is encountered, or a data error is encountered.
45 When large enough input and output buffers are supplied to inflate(), for
46 example, a 16K input buffer and a 64K output buffer, more than 95% of the
47 inflate execution time is spent in this routine.
48
49 Entry assumptions:
50
51 state->mode == LEN
52 strm->avail_in >= 6
53 strm->avail_out >= 258
54 start >= strm->avail_out
55 state->bits < 8
56
57 On return, state->mode is one of:
58
59 LEN -- ran out of enough output space or enough available input
60 TYPE -- reached end of block code, inflate() to interpret next block
61 BAD -- error in block data
62
63 Notes:
64
65 - The maximum input bits used by a length/distance pair is 15 bits for the
66 length code, 5 bits for the length extra, 15 bits for the distance code,
67 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
68 Therefore if strm->avail_in >= 6, then there is enough input to avoid
69 checking for available input while decoding.
70
71 - The maximum bytes that a single length/distance pair can output is 258
72 bytes, which is the maximum length that can be coded. inflate_fast()
73 requires strm->avail_out >= 258 for each loop to avoid checking for
74 output space.
75
76 @param start inflate()'s starting value for strm->avail_out
77 */
78 void
inflate_fast(z_streamp strm,unsigned start)79 inflate_fast(z_streamp strm, unsigned start)
80 {
81 struct inflate_state FAR *state;
82 unsigned char FAR *in; /* local strm->next_in */
83 unsigned char FAR *last; /* while in < last, enough input available */
84 unsigned char FAR *out; /* local strm->next_out */
85 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
86 unsigned char FAR *end; /* while out < end, enough space available */
87 #ifdef INFLATE_STRICT
88 unsigned dmax; /* maximum distance from zlib header */
89 #endif
90 unsigned wsize; /* window size or zero if not using window */
91 unsigned whave; /* valid bytes in the window */
92 unsigned write; /* window write index */
93 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
94 unsigned long hold; /* local strm->hold */
95 unsigned bits; /* local strm->bits */
96 code const FAR *lcode; /* local strm->lencode */
97 code const FAR *dcode; /* local strm->distcode */
98 unsigned lmask; /* mask for first level of length codes */
99 unsigned dmask; /* mask for first level of distance codes */
100 code this; /* retrieved table entry */
101 unsigned op; /* code bits, operation, extra bits, or */
102 /* window position, window bytes to copy */
103 unsigned len; /* match length, unused bytes */
104 unsigned dist; /* match distance */
105 unsigned char FAR *from; /* where to copy match from */
106
107 /* copy state to local variables */
108 state = (struct inflate_state FAR *)strm->state;
109 in = strm->next_in;
110 last = in + (strm->avail_in - 5);
111 out = strm->next_out;
112 beg = out - (start - strm->avail_out);
113 end = out + (strm->avail_out - 257);
114 #ifdef INFLATE_STRICT
115 dmax = state->dmax;
116 #endif
117 wsize = state->wsize;
118 whave = state->whave;
119 write = state->write;
120 window = state->window;
121 hold = state->hold;
122 bits = state->bits;
123 lcode = state->lencode;
124 dcode = state->distcode;
125 lmask = (1U << state->lenbits) - 1;
126 dmask = (1U << state->distbits) - 1;
127
128 /* decode literals and length/distances until end-of-block or not enough
129 input data or output space */
130 do {
131 if (bits < 15) {
132 hold += (unsigned long)(*in++) << bits;
133 bits += 8;
134 hold += (unsigned long)(*in++) << bits;
135 bits += 8;
136 }
137 this = lcode[hold & lmask];
138 dolen:
139 op = (unsigned)(this.bits);
140 hold >>= op;
141 bits -= op;
142 op = (unsigned)(this.op);
143 if (op == 0) { /* literal */
144 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
145 "inflate: literal '%c'\n" :
146 "inflate: literal 0x%02x\n", this.val));
147 *out++ = (unsigned char)(this.val);
148 }
149 else if (op & 16) { /* length base */
150 len = (unsigned)(this.val);
151 op &= 15; /* number of extra bits */
152 if (op) {
153 if (bits < op) {
154 hold += (unsigned long)(*in++) << bits;
155 bits += 8;
156 }
157 len += (unsigned)hold & ((1U << op) - 1);
158 hold >>= op;
159 bits -= op;
160 }
161 Tracevv((stderr, "inflate: length %u\n", len));
162 if (bits < 15) {
163 hold += (unsigned long)(*in++) << bits;
164 bits += 8;
165 hold += (unsigned long)(*in++) << bits;
166 bits += 8;
167 }
168 this = dcode[hold & dmask];
169 dodist:
170 op = (unsigned)(this.bits);
171 hold >>= op;
172 bits -= op;
173 op = (unsigned)(this.op);
174 if (op & 16) { /* distance base */
175 dist = (unsigned)(this.val);
176 op &= 15; /* number of extra bits */
177 if (bits < op) {
178 hold += (unsigned long)(*in++) << bits;
179 bits += 8;
180 if (bits < op) {
181 hold += (unsigned long)(*in++) << bits;
182 bits += 8;
183 }
184 }
185 dist += (unsigned)hold & ((1U << op) - 1);
186 #ifdef INFLATE_STRICT
187 if (dist > dmax) {
188 strm->msg = (char *)"invalid distance too far back";
189 state->mode = BAD;
190 break;
191 }
192 #endif
193 hold >>= op;
194 bits -= op;
195 Tracevv((stderr, "inflate: distance %u\n", dist));
196 op = (unsigned)(out - beg); /* max distance in output */
197 if (dist > op) { /* see if copy from window */
198 op = dist - op; /* distance back in window */
199 if (op > whave) {
200 strm->msg = (char *)"invalid distance too far back";
201 state->mode = BAD;
202 break;
203 }
204 from = window;
205 if (write == 0) { /* very common case */
206 from += wsize - op;
207 if (op < len) { /* some from window */
208 len -= op;
209 do {
210 *out++ = *from++;
211 } while (--op);
212 from = out - dist; /* rest from output */
213 }
214 }
215 else if (write < op) { /* wrap around window */
216 from += wsize + write - op;
217 op -= write;
218 if (op < len) { /* some from end of window */
219 len -= op;
220 do {
221 *out++ = *from++;
222 } while (--op);
223 from = window;
224 if (write < len) { /* some from start of window */
225 op = write;
226 len -= op;
227 do {
228 *out++ = *from++;
229 } while (--op);
230 from = out - dist; /* rest from output */
231 }
232 }
233 }
234 else { /* contiguous in window */
235 from += write - op;
236 if (op < len) { /* some from window */
237 len -= op;
238 do {
239 *out++ = *from++;
240 } while (--op);
241 from = out - dist; /* rest from output */
242 }
243 }
244 while (len > 2) {
245 *out++ = *from++;
246 *out++ = *from++;
247 *out++ = *from++;
248 len -= 3;
249 }
250 if (len) {
251 *out++ = *from++;
252 if (len > 1)
253 *out++ = *from++;
254 }
255 }
256 else {
257 from = out - dist; /* copy direct from output */
258 do { /* minimum length is three */
259 *out++ = *from++;
260 *out++ = *from++;
261 *out++ = *from++;
262 len -= 3;
263 } while (len > 2);
264 if (len) {
265 *out++ = *from++;
266 if (len > 1)
267 *out++ = *from++;
268 }
269 }
270 }
271 else if ((op & 64) == 0) { /* 2nd level distance code */
272 this = dcode[this.val + (hold & ((1U << op) - 1))];
273 goto dodist;
274 }
275 else {
276 strm->msg = (char *)"invalid distance code";
277 state->mode = BAD;
278 break;
279 }
280 }
281 else if ((op & 64) == 0) { /* 2nd level length code */
282 this = lcode[this.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 strm->msg = (char *)"invalid literal/length code";
292 state->mode = BAD;
293 break;
294 }
295 } while (in < last && out < end);
296
297 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
298 len = bits >> 3;
299 in -= len;
300 bits -= len << 3;
301 hold &= (1U << bits) - 1;
302
303 /* update state and return */
304 strm->next_in = in;
305 strm->next_out = out;
306 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
307 strm->avail_out = (unsigned)(out < end ?
308 257 + (end - out) : 257 - (out - end));
309 state->hold = hold;
310 state->bits = bits;
311 return;
312 }
313
314 /*
315 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
316 - Using bit fields for code structure
317 - Different op definition to avoid & for extra bits (do & for table bits)
318 - Three separate decoding do-loops for direct, window, and write == 0
319 - Special case for distance > 1 copies to do overlapped load and store copy
320 - Explicit branch predictions (based on measured branch probabilities)
321 - Deferring match copy and interspersed it with decoding subsequent codes
322 - Swapping literal/length else
323 - Swapping window/direct else
324 - Larger unrolled copy loops (three is about right)
325 - Moving len -= 3 statement into middle of loop
326 */
327
328 #endif /* !ASMINF */
329