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 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 state = (struct inflate_state FAR *)strm->state;
100 in = strm->next_in - OFF;
101 last = in + (strm->avail_in - 5);
102 out = strm->next_out - OFF;
103 beg = out - (start - strm->avail_out);
104 end = out + (strm->avail_out - 257);
105 #ifdef INFLATE_STRICT
106 dmax = state->dmax;
107 #endif
108 wsize = state->wsize;
109 whave = state->whave;
110 write = state->write;
111 window = state->window;
112 hold = state->hold;
113 bits = state->bits;
114 lcode = state->lencode;
115 dcode = state->distcode;
116 lmask = (1U << state->lenbits) - 1;
117 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 do {
122 if (bits < 15) {
123 hold += (unsigned long)(PUP(in)) << bits;
124 bits += 8;
125 hold += (unsigned long)(PUP(in)) << bits;
126 bits += 8;
127 }
128 this = lcode[hold & lmask];
129 dolen:
130 op = (unsigned)(this.bits);
131 hold >>= op;
132 bits -= op;
133 op = (unsigned)(this.op);
134 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 PUP(out) = (unsigned char)(this.val);
139 }
140 else if (op & 16) { /* length base */
141 len = (unsigned)(this.val);
142 op &= 15; /* number of extra bits */
143 if (op) {
144 if (bits < op) {
145 hold += (unsigned long)(PUP(in)) << bits;
146 bits += 8;
147 }
148 len += (unsigned)hold & ((1U << op) - 1);
149 hold >>= op;
150 bits -= op;
151 }
152 Tracevv((stderr, "inflate: length %u\n", len));
153 if (bits < 15) {
154 hold += (unsigned long)(PUP(in)) << bits;
155 bits += 8;
156 hold += (unsigned long)(PUP(in)) << bits;
157 bits += 8;
158 }
159 this = dcode[hold & dmask];
160 dodist:
161 op = (unsigned)(this.bits);
162 hold >>= op;
163 bits -= op;
164 op = (unsigned)(this.op);
165 if (op & 16) { /* distance base */
166 dist = (unsigned)(this.val);
167 op &= 15; /* number of extra bits */
168 if (bits < op) {
169 hold += (unsigned long)(PUP(in)) << bits;
170 bits += 8;
171 if (bits < op) {
172 hold += (unsigned long)(PUP(in)) << bits;
173 bits += 8;
174 }
175 }
176 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 hold >>= op;
185 bits -= op;
186 Tracevv((stderr, "inflate: distance %u\n", dist));
187 op = (unsigned)(out - beg); /* max distance in output */
188 if (dist > op) { /* see if copy from window */
189 op = dist - op; /* distance back in window */
190 if (op > whave) {
191 #ifdef SMALL
192 strm->msg = "error";
193 #else
194 strm->msg = (char *)"invalid distance too far back";
195 #endif
196 state->mode = BAD;
197 break;
198 }
199 from = window - OFF;
200 if (write == 0) { /* very common case */
201 from += wsize - op;
202 if (op < len) { /* some from window */
203 len -= op;
204 do {
205 PUP(out) = PUP(from);
206 } while (--op);
207 from = out - dist; /* rest from output */
208 }
209 }
210 else if (write < op) { /* wrap around window */
211 from += wsize + write - op;
212 op -= write;
213 if (op < len) { /* some from end of window */
214 len -= op;
215 do {
216 PUP(out) = PUP(from);
217 } while (--op);
218 from = window - OFF;
219 if (write < len) { /* some from start of window */
220 op = write;
221 len -= op;
222 do {
223 PUP(out) = PUP(from);
224 } while (--op);
225 from = out - dist; /* rest from output */
226 }
227 }
228 }
229 else { /* contiguous in window */
230 from += write - op;
231 if (op < len) { /* some from window */
232 len -= op;
233 do {
234 PUP(out) = PUP(from);
235 } while (--op);
236 from = out - dist; /* rest from output */
237 }
238 }
239 while (len > 2) {
240 PUP(out) = PUP(from);
241 PUP(out) = PUP(from);
242 PUP(out) = PUP(from);
243 len -= 3;
244 }
245 if (len) {
246 PUP(out) = PUP(from);
247 if (len > 1)
248 PUP(out) = PUP(from);
249 }
250 }
251 else {
252 from = out - dist; /* copy direct from output */
253 do { /* minimum length is three */
254 PUP(out) = PUP(from);
255 PUP(out) = PUP(from);
256 PUP(out) = PUP(from);
257 len -= 3;
258 } while (len > 2);
259 if (len) {
260 PUP(out) = PUP(from);
261 if (len > 1)
262 PUP(out) = PUP(from);
263 }
264 }
265 }
266 else if ((op & 64) == 0) { /* 2nd level distance code */
267 this = dcode[this.val + (hold & ((1U << op) - 1))];
268 goto dodist;
269 }
270 else {
271 #ifdef SMALL
272 strm->msg = "error";
273 #else
274 strm->msg = (char *)"invalid distance code";
275 #endif
276 state->mode = BAD;
277 break;
278 }
279 }
280 else if ((op & 64) == 0) { /* 2nd level length code */
281 this = lcode[this.val + (hold & ((1U << op) - 1))];
282 goto dolen;
283 }
284 else if (op & 32) { /* end-of-block */
285 Tracevv((stderr, "inflate: end of block\n"));
286 state->mode = TYPE;
287 break;
288 }
289 else {
290 #ifdef SMALL
291 strm->msg = "error";
292 #else
293 strm->msg = (char *)"invalid literal/length code";
294 #endif
295 state->mode = BAD;
296 break;
297 }
298 } while (in < last && out < end);
299
300 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
301 len = bits >> 3;
302 in -= len;
303 bits -= len << 3;
304 hold &= (1U << bits) - 1;
305
306 /* update state and return */
307 strm->next_in = in + OFF;
308 strm->next_out = out + OFF;
309 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
310 strm->avail_out = (unsigned)(out < end ?
311 257 + (end - out) : 257 - (out - end));
312 state->hold = hold;
313 state->bits = bits;
314 return;
315 }
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 */