Line data Source code
1 : /* $OpenBSD: inffast.c,v 1.11 2005/07/20 15:56:46 millert Exp $ */
2 : /* inffast.c -- fast decoding
3 : * Copyright (C) 1995-2004 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 : #ifndef ASMINF
13 :
14 : /* Allow machine dependent optimization for post-increment or pre-increment.
15 : Based on testing to date,
16 : Pre-increment preferred for:
17 : - PowerPC G3 (Adler)
18 : - MIPS R5000 (Randers-Pehrson)
19 : Post-increment preferred for:
20 : - none
21 : No measurable difference:
22 : - Pentium III (Anderson)
23 : - M68060 (Nikl)
24 : */
25 : #ifdef POSTINC
26 : # define OFF 0
27 : # define PUP(a) *(a)++
28 : #else
29 : # define OFF 1
30 : # define PUP(a) *++(a)
31 : #endif
32 :
33 : /*
34 : Decode literal, length, and distance codes and write out the resulting
35 : literal and match bytes until either not enough input or output is
36 : available, an end-of-block is encountered, or a data error is encountered.
37 : When large enough input and output buffers are supplied to inflate(), for
38 : example, a 16K input buffer and a 64K output buffer, more than 95% of the
39 : inflate execution time is spent in this routine.
40 :
41 : Entry assumptions:
42 :
43 : state->mode == LEN
44 : strm->avail_in >= 6
45 : strm->avail_out >= 258
46 : start >= strm->avail_out
47 : state->bits < 8
48 :
49 : On return, state->mode is one of:
50 :
51 : LEN -- ran out of enough output space or enough available input
52 : TYPE -- reached end of block code, inflate() to interpret next block
53 : BAD -- error in block data
54 :
55 : Notes:
56 :
57 : - The maximum input bits used by a length/distance pair is 15 bits for the
58 : length code, 5 bits for the length extra, 15 bits for the distance code,
59 : and 13 bits for the distance extra. This totals 48 bits, or six bytes.
60 : Therefore if strm->avail_in >= 6, then there is enough input to avoid
61 : checking for available input while decoding.
62 :
63 : - The maximum bytes that a single length/distance pair can output is 258
64 : bytes, which is the maximum length that can be coded. inflate_fast()
65 : requires strm->avail_out >= 258 for each loop to avoid checking for
66 : output space.
67 : */
68 0 : void inflate_fast(strm, start)
69 : z_streamp strm;
70 : unsigned start; /* inflate()'s starting value for strm->avail_out */
71 : {
72 : struct inflate_state FAR *state;
73 : unsigned char FAR *in; /* local strm->next_in */
74 : unsigned char FAR *last; /* while in < last, enough input available */
75 : unsigned char FAR *out; /* local strm->next_out */
76 : unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
77 : unsigned char FAR *end; /* while out < end, enough space available */
78 : #ifdef INFLATE_STRICT
79 : unsigned dmax; /* maximum distance from zlib header */
80 : #endif
81 : unsigned wsize; /* window size or zero if not using window */
82 : unsigned whave; /* valid bytes in the window */
83 : unsigned write; /* window write index */
84 : unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
85 : unsigned long hold; /* local strm->hold */
86 : unsigned bits; /* local strm->bits */
87 : code const FAR *lcode; /* local strm->lencode */
88 : code const FAR *dcode; /* local strm->distcode */
89 : unsigned lmask; /* mask for first level of length codes */
90 : unsigned dmask; /* mask for first level of distance codes */
91 : code this; /* retrieved table entry */
92 : unsigned op; /* code bits, operation, extra bits, or */
93 : /* window position, window bytes to copy */
94 : unsigned len; /* match length, unused bytes */
95 : unsigned dist; /* match distance */
96 : unsigned char FAR *from; /* where to copy match from */
97 :
98 : /* copy state to local variables */
99 0 : state = (struct inflate_state FAR *)strm->state;
100 0 : in = strm->next_in - OFF;
101 0 : last = in + (strm->avail_in - 5);
102 0 : out = strm->next_out - OFF;
103 0 : beg = out - (start - strm->avail_out);
104 0 : end = out + (strm->avail_out - 257);
105 : #ifdef INFLATE_STRICT
106 : dmax = state->dmax;
107 : #endif
108 0 : wsize = state->wsize;
109 0 : whave = state->whave;
110 0 : write = state->write;
111 0 : window = state->window;
112 0 : hold = state->hold;
113 0 : bits = state->bits;
114 0 : lcode = state->lencode;
115 0 : dcode = state->distcode;
116 0 : lmask = (1U << state->lenbits) - 1;
117 0 : dmask = (1U << state->distbits) - 1;
118 :
119 : /* decode literals and length/distances until end-of-block or not enough
120 : input data or output space */
121 0 : do {
122 0 : if (bits < 15) {
123 0 : hold += (unsigned long)(PUP(in)) << bits;
124 0 : bits += 8;
125 0 : hold += (unsigned long)(PUP(in)) << bits;
126 0 : bits += 8;
127 0 : }
128 0 : this = lcode[hold & lmask];
129 : dolen:
130 0 : op = (unsigned)(this.bits);
131 0 : hold >>= op;
132 0 : bits -= op;
133 0 : op = (unsigned)(this.op);
134 0 : if (op == 0) { /* literal */
135 : Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
136 : "inflate: literal '%c'\n" :
137 : "inflate: literal 0x%02x\n", this.val));
138 0 : PUP(out) = (unsigned char)(this.val);
139 0 : }
140 0 : else if (op & 16) { /* length base */
141 0 : len = (unsigned)(this.val);
142 0 : op &= 15; /* number of extra bits */
143 0 : if (op) {
144 0 : if (bits < op) {
145 0 : hold += (unsigned long)(PUP(in)) << bits;
146 0 : bits += 8;
147 0 : }
148 0 : len += (unsigned)hold & ((1U << op) - 1);
149 0 : hold >>= op;
150 0 : bits -= op;
151 0 : }
152 : Tracevv((stderr, "inflate: length %u\n", len));
153 0 : if (bits < 15) {
154 0 : hold += (unsigned long)(PUP(in)) << bits;
155 0 : bits += 8;
156 0 : hold += (unsigned long)(PUP(in)) << bits;
157 0 : bits += 8;
158 0 : }
159 0 : this = dcode[hold & dmask];
160 : dodist:
161 0 : op = (unsigned)(this.bits);
162 0 : hold >>= op;
163 0 : bits -= op;
164 0 : op = (unsigned)(this.op);
165 0 : if (op & 16) { /* distance base */
166 0 : dist = (unsigned)(this.val);
167 0 : op &= 15; /* number of extra bits */
168 0 : if (bits < op) {
169 0 : hold += (unsigned long)(PUP(in)) << bits;
170 0 : bits += 8;
171 0 : if (bits < op) {
172 0 : hold += (unsigned long)(PUP(in)) << bits;
173 0 : bits += 8;
174 0 : }
175 : }
176 0 : dist += (unsigned)hold & ((1U << op) - 1);
177 : #ifdef INFLATE_STRICT
178 : if (dist > dmax) {
179 : strm->msg = (char *)"invalid distance too far back";
180 : state->mode = BAD;
181 : break;
182 : }
183 : #endif
184 0 : hold >>= op;
185 0 : bits -= op;
186 : Tracevv((stderr, "inflate: distance %u\n", dist));
187 0 : op = (unsigned)(out - beg); /* max distance in output */
188 0 : if (dist > op) { /* see if copy from window */
189 0 : op = dist - op; /* distance back in window */
190 0 : if (op > whave) {
191 : #ifdef SMALL
192 : strm->msg = "error";
193 : #else
194 0 : strm->msg = (char *)"invalid distance too far back";
195 : #endif
196 0 : state->mode = BAD;
197 0 : break;
198 : }
199 0 : from = window - OFF;
200 0 : if (write == 0) { /* very common case */
201 0 : from += wsize - op;
202 0 : if (op < len) { /* some from window */
203 0 : len -= op;
204 0 : do {
205 0 : PUP(out) = PUP(from);
206 0 : } while (--op);
207 0 : from = out - dist; /* rest from output */
208 0 : }
209 : }
210 0 : else if (write < op) { /* wrap around window */
211 0 : from += wsize + write - op;
212 0 : op -= write;
213 0 : if (op < len) { /* some from end of window */
214 0 : len -= op;
215 0 : do {
216 0 : PUP(out) = PUP(from);
217 0 : } while (--op);
218 : from = window - OFF;
219 0 : if (write < len) { /* some from start of window */
220 : op = write;
221 0 : len -= op;
222 0 : do {
223 0 : PUP(out) = PUP(from);
224 0 : } while (--op);
225 0 : from = out - dist; /* rest from output */
226 0 : }
227 : }
228 : }
229 : else { /* contiguous in window */
230 0 : from += write - op;
231 0 : if (op < len) { /* some from window */
232 0 : len -= op;
233 0 : do {
234 0 : PUP(out) = PUP(from);
235 0 : } while (--op);
236 0 : from = out - dist; /* rest from output */
237 0 : }
238 : }
239 0 : while (len > 2) {
240 0 : PUP(out) = PUP(from);
241 0 : PUP(out) = PUP(from);
242 0 : PUP(out) = PUP(from);
243 0 : len -= 3;
244 : }
245 0 : if (len) {
246 0 : PUP(out) = PUP(from);
247 0 : if (len > 1)
248 0 : PUP(out) = PUP(from);
249 : }
250 : }
251 : else {
252 0 : from = out - dist; /* copy direct from output */
253 0 : do { /* minimum length is three */
254 0 : PUP(out) = PUP(from);
255 0 : PUP(out) = PUP(from);
256 0 : PUP(out) = PUP(from);
257 0 : len -= 3;
258 0 : } while (len > 2);
259 0 : if (len) {
260 0 : PUP(out) = PUP(from);
261 0 : if (len > 1)
262 0 : PUP(out) = PUP(from);
263 : }
264 : }
265 : }
266 0 : else if ((op & 64) == 0) { /* 2nd level distance code */
267 0 : this = dcode[this.val + (hold & ((1U << op) - 1))];
268 0 : goto dodist;
269 : }
270 : else {
271 : #ifdef SMALL
272 : strm->msg = "error";
273 : #else
274 0 : strm->msg = (char *)"invalid distance code";
275 : #endif
276 0 : state->mode = BAD;
277 0 : break;
278 : }
279 : }
280 0 : else if ((op & 64) == 0) { /* 2nd level length code */
281 0 : this = lcode[this.val + (hold & ((1U << op) - 1))];
282 0 : goto dolen;
283 : }
284 0 : else if (op & 32) { /* end-of-block */
285 : Tracevv((stderr, "inflate: end of block\n"));
286 0 : state->mode = TYPE;
287 0 : break;
288 : }
289 : else {
290 : #ifdef SMALL
291 : strm->msg = "error";
292 : #else
293 0 : strm->msg = (char *)"invalid literal/length code";
294 : #endif
295 0 : state->mode = BAD;
296 0 : break;
297 : }
298 0 : } while (in < last && out < end);
299 :
300 : /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
301 0 : len = bits >> 3;
302 0 : in -= len;
303 0 : bits -= len << 3;
304 0 : hold &= (1U << bits) - 1;
305 :
306 : /* update state and return */
307 0 : strm->next_in = in + OFF;
308 0 : strm->next_out = out + OFF;
309 0 : strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
310 0 : strm->avail_out = (unsigned)(out < end ?
311 0 : 257 + (end - out) : 257 - (out - end));
312 0 : state->hold = hold;
313 0 : state->bits = bits;
314 : return;
315 0 : }
316 :
317 : /*
318 : inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
319 : - Using bit fields for code structure
320 : - Different op definition to avoid & for extra bits (do & for table bits)
321 : - Three separate decoding do-loops for direct, window, and write == 0
322 : - Special case for distance > 1 copies to do overlapped load and store copy
323 : - Explicit branch predictions (based on measured branch probabilities)
324 : - Deferring match copy and interspersed it with decoding subsequent codes
325 : - Swapping literal/length else
326 : - Swapping window/direct else
327 : - Larger unrolled copy loops (three is about right)
328 : - Moving len -= 3 statement into middle of loop
329 : */
330 :
331 : #endif /* !ASMINF */
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