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[apple/xnu.git] / libkern / zlib / inffast.c
1 /*
2 * Copyright (c) 2008 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
24 * limitations under the License.
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 #if defined __x86_64__ || defined __i386__ || defined _ARM_ARCH_6
35
36 // dummy definition, for x86_64 or i386 or armv6 or up, compile code from inffastS.s
37 typedef char DummyDefinition;
38
39 #else // architecture
40
41
42 #include "zutil.h"
43 #include "inftrees.h"
44 #include "inflate.h"
45 #include "inffast.h"
46
47 #ifndef ASMINF
48
49 /* Allow machine dependent optimization for post-increment or pre-increment.
50 Based on testing to date,
51 Pre-increment preferred for:
52 - PowerPC G3 (Adler)
53 - MIPS R5000 (Randers-Pehrson)
54 Post-increment preferred for:
55 - none
56 No measurable difference:
57 - Pentium III (Anderson)
58 - M68060 (Nikl)
59 */
60 #ifdef POSTINC
61 # define OFF 0
62 # define PUP(a) *(a)++
63 #else
64 # define OFF 1
65 # define PUP(a) *++(a)
66 #endif
67
68 /*
69 Decode literal, length, and distance codes and write out the resulting
70 literal and match bytes until either not enough input or output is
71 available, an end-of-block is encountered, or a data error is encountered.
72 When large enough input and output buffers are supplied to inflate(), for
73 example, a 16K input buffer and a 64K output buffer, more than 95% of the
74 inflate execution time is spent in this routine.
75
76 Entry assumptions:
77
78 state->mode == LEN
79 strm->avail_in >= 6
80 strm->avail_out >= 258
81 start >= strm->avail_out
82 state->bits < 8
83
84 On return, state->mode is one of:
85
86 LEN -- ran out of enough output space or enough available input
87 TYPE -- reached end of block code, inflate() to interpret next block
88 BAD -- error in block data
89
90 Notes:
91
92 - The maximum input bits used by a length/distance pair is 15 bits for the
93 length code, 5 bits for the length extra, 15 bits for the distance code,
94 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
95 Therefore if strm->avail_in >= 6, then there is enough input to avoid
96 checking for available input while decoding.
97
98 - The maximum bytes that a single length/distance pair can output is 258
99 bytes, which is the maximum length that can be coded. inflate_fast()
100 requires strm->avail_out >= 258 for each loop to avoid checking for
101 output space.
102 */
103 void inflate_fast(strm, start)
104 z_streamp strm;
105 unsigned start; /* inflate()'s starting value for strm->avail_out */
106 {
107 struct inflate_state FAR *state;
108 unsigned char FAR *in; /* local strm->next_in */
109 unsigned char FAR *last; /* while in < last, enough input available */
110 unsigned char FAR *out; /* local strm->next_out */
111 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
112 unsigned char FAR *end; /* while out < end, enough space available */
113 #ifdef INFLATE_STRICT
114 unsigned dmax; /* maximum distance from zlib header */
115 #endif
116 unsigned wsize; /* window size or zero if not using window */
117 unsigned whave; /* valid bytes in the window */
118 unsigned write; /* window write index */
119 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
120 unsigned long hold; /* local strm->hold */
121 unsigned bits; /* local strm->bits */
122 code const FAR *lcode; /* local strm->lencode */
123 code const FAR *dcode; /* local strm->distcode */
124 unsigned lmask; /* mask for first level of length codes */
125 unsigned dmask; /* mask for first level of distance codes */
126 code this; /* retrieved table entry */
127 unsigned op; /* code bits, operation, extra bits, or */
128 /* window position, window bytes to copy */
129 unsigned len; /* match length, unused bytes */
130 unsigned dist; /* match distance */
131 unsigned char FAR *from; /* where to copy match from */
132
133 /* copy state to local variables */
134 state = (struct inflate_state FAR *)strm->state;
135 in = strm->next_in - OFF;
136 last = in + (strm->avail_in - 5);
137 out = strm->next_out - OFF;
138 beg = out - (start - strm->avail_out);
139 end = out + (strm->avail_out - 257);
140 #ifdef INFLATE_STRICT
141 dmax = state->dmax;
142 #endif
143 wsize = state->wsize;
144 whave = state->whave;
145 write = state->write;
146 window = state->window;
147 hold = state->hold;
148 bits = state->bits;
149 lcode = state->lencode;
150 dcode = state->distcode;
151 lmask = (1U << state->lenbits) - 1;
152 dmask = (1U << state->distbits) - 1;
153
154 /* decode literals and length/distances until end-of-block or not enough
155 input data or output space */
156 do {
157 if (bits < 15) {
158 hold += (unsigned long)(PUP(in)) << bits;
159 bits += 8;
160 hold += (unsigned long)(PUP(in)) << bits;
161 bits += 8;
162 }
163 this = lcode[hold & lmask];
164 dolen:
165 op = (unsigned)(this.bits);
166 hold >>= op;
167 bits -= op;
168 op = (unsigned)(this.op);
169 if (op == 0) { /* literal */
170 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
171 "inflate: literal '%c'\n" :
172 "inflate: literal 0x%02x\n", this.val));
173 PUP(out) = (unsigned char)(this.val);
174 }
175 else if (op & 16) { /* length base */
176 len = (unsigned)(this.val);
177 op &= 15; /* number of extra bits */
178 if (op) {
179 if (bits < op) {
180 hold += (unsigned long)(PUP(in)) << bits;
181 bits += 8;
182 }
183 len += (unsigned)hold & ((1U << op) - 1);
184 hold >>= op;
185 bits -= op;
186 }
187 Tracevv((stderr, "inflate: length %u\n", len));
188 if (bits < 15) {
189 hold += (unsigned long)(PUP(in)) << bits;
190 bits += 8;
191 hold += (unsigned long)(PUP(in)) << bits;
192 bits += 8;
193 }
194 this = dcode[hold & dmask];
195 dodist:
196 op = (unsigned)(this.bits);
197 hold >>= op;
198 bits -= op;
199 op = (unsigned)(this.op);
200 if (op & 16) { /* distance base */
201 dist = (unsigned)(this.val);
202 op &= 15; /* number of extra bits */
203 if (bits < op) {
204 hold += (unsigned long)(PUP(in)) << bits;
205 bits += 8;
206 if (bits < op) {
207 hold += (unsigned long)(PUP(in)) << bits;
208 bits += 8;
209 }
210 }
211 dist += (unsigned)hold & ((1U << op) - 1);
212 #ifdef INFLATE_STRICT
213 if (dist > dmax) {
214 strm->msg = (char *)"invalid distance too far back";
215 state->mode = BAD;
216 break;
217 }
218 #endif
219 hold >>= op;
220 bits -= op;
221 Tracevv((stderr, "inflate: distance %u\n", dist));
222 op = (unsigned)(out - beg); /* max distance in output */
223 if (dist > op) { /* see if copy from window */
224 op = dist - op; /* distance back in window */
225 if (op > whave) {
226 strm->msg = (char *)"invalid distance too far back";
227 state->mode = BAD;
228 break;
229 }
230 from = window - OFF;
231 if (write == 0) { /* very common case */
232 from += wsize - op;
233 if (op < len) { /* some from window */
234 len -= op;
235 do {
236 PUP(out) = PUP(from);
237 } while (--op);
238 from = out - dist; /* rest from output */
239 }
240 }
241 else if (write < op) { /* wrap around window */
242 from += wsize + write - op;
243 op -= write;
244 if (op < len) { /* some from end of window */
245 len -= op;
246 do {
247 PUP(out) = PUP(from);
248 } while (--op);
249 from = window - OFF;
250 if (write < len) { /* some from start of window */
251 op = write;
252 len -= op;
253 do {
254 PUP(out) = PUP(from);
255 } while (--op);
256 from = out - dist; /* rest from output */
257 }
258 }
259 }
260 else { /* contiguous in window */
261 from += write - op;
262 if (op < len) { /* some from window */
263 len -= op;
264 do {
265 PUP(out) = PUP(from);
266 } while (--op);
267 from = out - dist; /* rest from output */
268 }
269 }
270 while (len > 2) {
271 PUP(out) = PUP(from);
272 PUP(out) = PUP(from);
273 PUP(out) = PUP(from);
274 len -= 3;
275 }
276 if (len) {
277 PUP(out) = PUP(from);
278 if (len > 1)
279 PUP(out) = PUP(from);
280 }
281 }
282 else {
283 from = out - dist; /* copy direct from output */
284 do { /* minimum length is three */
285 PUP(out) = PUP(from);
286 PUP(out) = PUP(from);
287 PUP(out) = PUP(from);
288 len -= 3;
289 } while (len > 2);
290 if (len) {
291 PUP(out) = PUP(from);
292 if (len > 1)
293 PUP(out) = PUP(from);
294 }
295 }
296 }
297 else if ((op & 64) == 0) { /* 2nd level distance code */
298 this = dcode[this.val + (hold & ((1U << op) - 1))];
299 goto dodist;
300 }
301 else {
302 strm->msg = (char *)"invalid distance code";
303 state->mode = BAD;
304 break;
305 }
306 }
307 else if ((op & 64) == 0) { /* 2nd level length code */
308 this = lcode[this.val + (hold & ((1U << op) - 1))];
309 goto dolen;
310 }
311 else if (op & 32) { /* end-of-block */
312 Tracevv((stderr, "inflate: end of block\n"));
313 state->mode = TYPE;
314 break;
315 }
316 else {
317 strm->msg = (char *)"invalid literal/length code";
318 state->mode = BAD;
319 break;
320 }
321 } while (in < last && out < end);
322
323 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
324 len = bits >> 3;
325 in -= len;
326 bits -= len << 3;
327 hold &= (1U << bits) - 1;
328
329 /* update state and return */
330 strm->next_in = in + OFF;
331 strm->next_out = out + OFF;
332 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
333 strm->avail_out = (unsigned)(out < end ?
334 257 + (end - out) : 257 - (out - end));
335 state->hold = hold;
336 state->bits = bits;
337 return;
338 }
339
340 /*
341 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
342 - Using bit fields for code structure
343 - Different op definition to avoid & for extra bits (do & for table bits)
344 - Three separate decoding do-loops for direct, window, and write == 0
345 - Special case for distance > 1 copies to do overlapped load and store copy
346 - Explicit branch predictions (based on measured branch probabilities)
347 - Deferring match copy and interspersed it with decoding subsequent codes
348 - Swapping literal/length else
349 - Swapping window/direct else
350 - Larger unrolled copy loops (three is about right)
351 - Moving len -= 3 statement into middle of loop
352 */
353
354 #endif /* !ASMINF */
355
356 #endif // architecture
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