1 /* inffast.c -- fast decoding
2 * Copyright (C) 1995-2004 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6 #include <linux/zutil.h>
7 #include "inftrees.h"
8 #include "inflate.h"
9 #include "inffast.h"
10
11 #ifndef ASMINF
12
13 /* Allow machine dependent optimization for post-increment or pre-increment.
14 Based on testing to date,
15 Pre-increment preferred for:
16 - PowerPC G3 (Adler)
17 - MIPS R5000 (Randers-Pehrson)
18 Post-increment preferred for:
19 - none
20 No measurable difference:
21 - Pentium III (Anderson)
22 - M68060 (Nikl)
23 */
24 union uu {
25 unsigned short us;
26 unsigned char b[2];
27 };
28
29 /* Endian independed version */
30 static inline unsigned short
31 get_unaligned16(const unsigned short *p)
32 {
33 union uu mm;
34 unsigned char *b = (unsigned char *)p;
35
36 mm.b[0] = b[0];
37 mm.b[1] = b[1];
38 return mm.us;
39 }
40
41 #ifdef POSTINC
42 # define OFF 0
43 # define PUP(a) *(a)++
44 # define UP_UNALIGNED(a) get_unaligned16((a)++)
45 #else
46 # define OFF 1
47 # define PUP(a) *++(a)
48 # define UP_UNALIGNED(a) get_unaligned16(++(a))
49 #endif
50
51 /*
52 Decode literal, length, and distance codes and write out the resulting
53 literal and match bytes until either not enough input or output is
54 available, an end-of-block is encountered, or a data error is encountered.
55 When large enough input and output buffers are supplied to inflate(), for
56 example, a 16K input buffer and a 64K output buffer, more than 95% of the
57 inflate execution time is spent in this routine.
58
59 Entry assumptions:
60
61 state->mode == LEN
62 strm->avail_in >= 6
63 strm->avail_out >= 258
64 start >= strm->avail_out
65 state->bits < 8
66
67 On return, state->mode is one of:
68
69 LEN -- ran out of enough output space or enough available input
70 TYPE -- reached end of block code, inflate() to interpret next block
71 BAD -- error in block data
72
73 Notes:
74
75 - The maximum input bits used by a length/distance pair is 15 bits for the
76 length code, 5 bits for the length extra, 15 bits for the distance code,
77 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
78 Therefore if strm->avail_in >= 6, then there is enough input to avoid
79 checking for available input while decoding.
80
81 - The maximum bytes that a single length/distance pair can output is 258
82 bytes, which is the maximum length that can be coded. inflate_fast()
83 requires strm->avail_out >= 258 for each loop to avoid checking for
84 output space.
85
86 - @start: inflate()'s starting value for strm->avail_out
87 */
88 void inflate_fast(z_streamp strm, unsigned start)
89 {
90 struct inflate_state *state;
91 const unsigned char *in; /* local strm->next_in */
92 const unsigned char *last; /* while in < last, enough input available */
93 unsigned char *out; /* local strm->next_out */
94 unsigned char *beg; /* inflate()'s initial strm->next_out */
95 unsigned char *end; /* while out < end, enough space available */
96 #ifdef INFLATE_STRICT
97 unsigned dmax; /* maximum distance from zlib header */
98 #endif
99 unsigned wsize; /* window size or zero if not using window */
100 unsigned whave; /* valid bytes in the window */
101 unsigned write; /* window write index */
102 unsigned char *window; /* allocated sliding window, if wsize != 0 */
103 unsigned long hold; /* local strm->hold */
104 unsigned bits; /* local strm->bits */
105 code const *lcode; /* local strm->lencode */
106 code const *dcode; /* local strm->distcode */
107 unsigned lmask; /* mask for first level of length codes */
108 unsigned dmask; /* mask for first level of distance codes */
109 code this; /* retrieved table entry */
110 unsigned op; /* code bits, operation, extra bits, or */
111 /* window position, window bytes to copy */
112 unsigned len; /* match length, unused bytes */
113 unsigned dist; /* match distance */
114 unsigned char *from; /* where to copy match from */
115
116 /* copy state to local variables */
117 state = (struct inflate_state *)strm->state;
118 in = strm->next_in - OFF;
119 last = in + (strm->avail_in - 5);
120 out = strm->next_out - OFF;
121 beg = out - (start - strm->avail_out);
122 end = out + (strm->avail_out - 257);
123 #ifdef INFLATE_STRICT
124 dmax = state->dmax;
125 #endif
126 wsize = state->wsize;
127 whave = state->whave;
128 write = state->write;
129 window = state->window;
130 hold = state->hold;
131 bits = state->bits;
132 lcode = state->lencode;
133 dcode = state->distcode;
134 lmask = (1U << state->lenbits) - 1;
135 dmask = (1U << state->distbits) - 1;
136
137 /* decode literals and length/distances until end-of-block or not enough
138 input data or output space */
139 do {
140 if (bits < 15) {
141 hold += (unsigned long)(PUP(in)) << bits;
142 bits += 8;
143 hold += (unsigned long)(PUP(in)) << bits;
144 bits += 8;
145 }
146 this = lcode[hold & lmask];
147 dolen:
148 op = (unsigned)(this.bits);
149 hold >>= op;
150 bits -= op;
151 op = (unsigned)(this.op);
152 if (op == 0) { /* literal */
153 PUP(out) = (unsigned char)(this.val);
154 }
155 else if (op & 16) { /* length base */
156 len = (unsigned)(this.val);
157 op &= 15; /* number of extra bits */
158 if (op) {
159 if (bits < op) {
160 hold += (unsigned long)(PUP(in)) << bits;
161 bits += 8;
162 }
163 len += (unsigned)hold & ((1U << op) - 1);
164 hold >>= op;
165 bits -= op;
166 }
167 if (bits < 15) {
168 hold += (unsigned long)(PUP(in)) << bits;
169 bits += 8;
170 hold += (unsigned long)(PUP(in)) << bits;
171 bits += 8;
172 }
173 this = dcode[hold & dmask];
174 dodist:
175 op = (unsigned)(this.bits);
176 hold >>= op;
177 bits -= op;
178 op = (unsigned)(this.op);
179 if (op & 16) { /* distance base */
180 dist = (unsigned)(this.val);
181 op &= 15; /* number of extra bits */
182 if (bits < op) {
183 hold += (unsigned long)(PUP(in)) << bits;
184 bits += 8;
185 if (bits < op) {
186 hold += (unsigned long)(PUP(in)) << bits;
187 bits += 8;
188 }
189 }
190 dist += (unsigned)hold & ((1U << op) - 1);
191 #ifdef INFLATE_STRICT
192 if (dist > dmax) {
193 strm->msg = (char *)"invalid distance too far back";
194 state->mode = BAD;
195 break;
196 }
197 #endif
198 hold >>= op;
199 bits -= op;
200 op = (unsigned)(out - beg); /* max distance in output */
201 if (dist > op) { /* see if copy from window */
202 op = dist - op; /* distance back in window */
203 if (op > whave) {
204 strm->msg = (char *)"invalid distance too far back";
205 state->mode = BAD;
206 break;
207 }
208 from = window - OFF;
209 if (write == 0) { /* very common case */
210 from += wsize - op;
211 if (op < len) { /* some from window */
212 len -= op;
213 do {
214 PUP(out) = PUP(from);
215 } while (--op);
216 from = out - dist; /* rest from output */
217 }
218 }
219 else if (write < op) { /* wrap around window */
220 from += wsize + write - op;
221 op -= write;
222 if (op < len) { /* some from end of window */
223 len -= op;
224 do {
225 PUP(out) = PUP(from);
226 } while (--op);
227 from = window - OFF;
228 if (write < len) { /* some from start of window */
229 op = write;
230 len -= op;
231 do {
232 PUP(out) = PUP(from);
233 } while (--op);
234 from = out - dist; /* rest from output */
235 }
236 }
237 }
238 else { /* contiguous in window */
239 from += write - op;
240 if (op < len) { /* some from window */
241 len -= op;
242 do {
243 PUP(out) = PUP(from);
244 } while (--op);
245 from = out - dist; /* rest from output */
246 }
247 }
248 while (len > 2) {
249 PUP(out) = PUP(from);
250 PUP(out) = PUP(from);
251 PUP(out) = PUP(from);
252 len -= 3;
253 }
254 if (len) {
255 PUP(out) = PUP(from);
256 if (len > 1)
257 PUP(out) = PUP(from);
258 }
259 }
260 else {
261 unsigned short *sout;
262 unsigned long loops;
263
264 from = out - dist; /* copy direct from output */
265 /* minimum length is three */
266 /* Align out addr */
267 if (!((long)(out - 1 + OFF) & 1)) {
268 PUP(out) = PUP(from);
269 len--;
270 }
271 sout = (unsigned short *)(out - OFF);
272 if (dist > 2) {
273 unsigned short *sfrom;
274
275 sfrom = (unsigned short *)(from - OFF);
276 loops = len >> 1;
277 do
278 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
279 PUP(sout) = PUP(sfrom);
280 #else
281 PUP(sout) = UP_UNALIGNED(sfrom);
282 #endif
283 while (--loops);
284 out = (unsigned char *)sout + OFF;
285 from = (unsigned char *)sfrom + OFF;
286 } else { /* dist == 1 or dist == 2 */
287 unsigned short pat16;
288
289 pat16 = *(sout-1+OFF);
290 if (dist == 1) {
291 union uu mm;
292 /* copy one char pattern to both bytes */
293 mm.us = pat16;
294 mm.b[0] = mm.b[1];
295 pat16 = mm.us;
296 }
297 loops = len >> 1;
298 do
299 PUP(sout) = pat16;
300 while (--loops);
301 out = (unsigned char *)sout + OFF;
302 }
303 if (len & 1)
304 PUP(out) = PUP(from);
305 }
306 }
307 else if ((op & 64) == 0) { /* 2nd level distance code */
308 this = dcode[this.val + (hold & ((1U << op) - 1))];
309 goto dodist;
310 }
311 else {
312 strm->msg = (char *)"invalid distance code";
313 state->mode = BAD;
314 break;
315 }
316 }
317 else if ((op & 64) == 0) { /* 2nd level length code */
318 this = lcode[this.val + (hold & ((1U << op) - 1))];
319 goto dolen;
320 }
321 else if (op & 32) { /* end-of-block */
322 state->mode = TYPE;
323 break;
324 }
325 else {
326 strm->msg = (char *)"invalid literal/length code";
327 state->mode = BAD;
328 break;
329 }
330 } while (in < last && out < end);
331
332 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
333 len = bits >> 3;
334 in -= len;
335 bits -= len << 3;
336 hold &= (1U << bits) - 1;
337
338 /* update state and return */
339 strm->next_in = in + OFF;
340 strm->next_out = out + OFF;
341 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
342 strm->avail_out = (unsigned)(out < end ?
343 257 + (end - out) : 257 - (out - end));
344 state->hold = hold;
345 state->bits = bits;
346 return;
347 }
348
349 /*
350 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
351 - Using bit fields for code structure
352 - Different op definition to avoid & for extra bits (do & for table bits)
353 - Three separate decoding do-loops for direct, window, and write == 0
354 - Special case for distance > 1 copies to do overlapped load and store copy
355 - Explicit branch predictions (based on measured branch probabilities)
356 - Deferring match copy and interspersed it with decoding subsequent codes
357 - Swapping literal/length else
358 - Swapping window/direct else
359 - Larger unrolled copy loops (three is about right)
360 - Moving len -= 3 statement into middle of loop
361 */
362
363 #endif /* !ASMINF */