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---
inffast.c (12568B)
---
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 "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 #ifdef POSTINC
25 # define OFF 0
26 # define PUP(a) *(a)++
27 #else
28 # define OFF 1
29 # define PUP(a) *++(a)
30 #endif
31
32 /*
33 Decode literal, length, and distance codes and write out the resulting
34 literal and match bytes until either not enough input or output is
35 available, an end-of-block is encountered, or a data error is encountered.
36 When large enough input and output buffers are supplied to inflate(), for
37 example, a 16K input buffer and a 64K output buffer, more than 95% of the
38 inflate execution time is spent in this routine.
39
40 Entry assumptions:
41
42 state->mode == LEN
43 strm->avail_in >= 6
44 strm->avail_out >= 258
45 start >= strm->avail_out
46 state->bits < 8
47
48 On return, state->mode is one of:
49
50 LEN -- ran out of enough output space or enough available input
51 TYPE -- reached end of block code, inflate() to interpret next block
52 BAD -- error in block data
53
54 Notes:
55
56 - The maximum input bits used by a length/distance pair is 15 bits for the
57 length code, 5 bits for the length extra, 15 bits for the distance code,
58 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
59 Therefore if strm->avail_in >= 6, then there is enough input to avoid
60 checking for available input while decoding.
61
62 - The maximum bytes that a single length/distance pair can output is 258
63 bytes, which is the maximum length that can be coded. inflate_fast()
64 requires strm->avail_out >= 258 for each loop to avoid checking for
65 output space.
66 */
67 void inflate_fast(strm, start)
68 z_streamp strm;
69 unsigned start; /* inflate()'s starting value for strm->avail_out */
70 {
71 struct inflate_state FAR *state;
72 unsigned char FAR *in; /* local strm->next_in */
73 unsigned char FAR *last; /* while in < last, enough input available */
74 unsigned char FAR *out; /* local strm->next_out */
75 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
76 unsigned char FAR *end; /* while out < end, enough space available */
77 #ifdef INFLATE_STRICT
78 unsigned dmax; /* maximum distance from zlib header */
79 #endif
80 unsigned wsize; /* window size or zero if not using window */
81 unsigned whave; /* valid bytes in the window */
82 unsigned write; /* window write index */
83 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
84 unsigned long hold; /* local strm->hold */
85 unsigned bits; /* local strm->bits */
86 code const FAR *lcode; /* local strm->lencode */
87 code const FAR *dcode; /* local strm->distcode */
88 unsigned lmask; /* mask for first level of length codes */
89 unsigned dmask; /* mask for first level of distance codes */
90 code this; /* retrieved table entry */
91 unsigned op; /* code bits, operation, extra bits, or */
92 /* window position, window bytes to copy */
93 unsigned len; /* match length, unused bytes */
94 unsigned dist; /* match distance */
95 unsigned char FAR *from; /* where to copy match from */
96
97 /* copy state to local variables */
98 state = (struct inflate_state FAR *)strm->state;
99 in = strm->next_in - OFF;
100 last = in + (strm->avail_in - 5);
101 out = strm->next_out - OFF;
102 beg = out - (start - strm->avail_out);
103 end = out + (strm->avail_out - 257);
104 #ifdef INFLATE_STRICT
105 dmax = state->dmax;
106 #endif
107 wsize = state->wsize;
108 whave = state->whave;
109 write = state->write;
110 window = state->window;
111 hold = state->hold;
112 bits = state->bits;
113 lcode = state->lencode;
114 dcode = state->distcode;
115 lmask = (1U << state->lenbits) - 1;
116 dmask = (1U << state->distbits) - 1;
117
118 /* decode literals and length/distances until end-of-block or not enough
119 input data or output space */
120 do {
121 if (bits < 15) {
122 hold += (unsigned long)(PUP(in)) << bits;
123 bits += 8;
124 hold += (unsigned long)(PUP(in)) << bits;
125 bits += 8;
126 }
127 this = lcode[hold & lmask];
128 dolen:
129 op = (unsigned)(this.bits);
130 hold >>= op;
131 bits -= op;
132 op = (unsigned)(this.op);
133 if (op == 0) { /* literal */
134 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
135 "inflate: literal '%c'\n" :
136 "inflate: literal 0x%02x\n", this.val));
137 PUP(out) = (unsigned char)(this.val);
138 }
139 else if (op & 16) { /* length base */
140 len = (unsigned)(this.val);
141 op &= 15; /* number of extra bits */
142 if (op) {
143 if (bits < op) {
144 hold += (unsigned long)(PUP(in)) << bits;
145 bits += 8;
146 }
147 len += (unsigned)hold & ((1U << op) - 1);
148 hold >>= op;
149 bits -= op;
150 }
151 Tracevv((stderr, "inflate: length %u\n", len));
152 if (bits < 15) {
153 hold += (unsigned long)(PUP(in)) << bits;
154 bits += 8;
155 hold += (unsigned long)(PUP(in)) << bits;
156 bits += 8;
157 }
158 this = dcode[hold & dmask];
159 dodist:
160 op = (unsigned)(this.bits);
161 hold >>= op;
162 bits -= op;
163 op = (unsigned)(this.op);
164 if (op & 16) { /* distance base */
165 dist = (unsigned)(this.val);
166 op &= 15; /* number of extra bits */
167 if (bits < op) {
168 hold += (unsigned long)(PUP(in)) << bits;
169 bits += 8;
170 if (bits < op) {
171 hold += (unsigned long)(PUP(in)) << bits;
172 bits += 8;
173 }
174 }
175 dist += (unsigned)hold & ((1U << op) - 1);
176 #ifdef INFLATE_STRICT
177 if (dist > dmax) {
178 strm->msg = (char *)"invalid distance too far back";
179 state->mode = BAD;
180 break;
181 }
182 #endif
183 hold >>= op;
184 bits -= op;
185 Tracevv((stderr, "inflate: distance %u\n", dist));
186 op = (unsigned)(out - beg); /* max distance in output */
187 if (dist > op) { /* see if copy from window */
188 op = dist - op; /* distance back in window */
189 if (op > whave) {
190 strm->msg = (char *)"invalid distance too far back";
191 state->mode = BAD;
192 break;
193 }
194 from = window - OFF;
195 if (write == 0) { /* very common case */
196 from += wsize - op;
197 if (op < len) { /* some from window */
198 len -= op;
199 do {
200 PUP(out) = PUP(from);
201 } while (--op);
202 from = out - dist; /* rest from output */
203 }
204 }
205 else if (write < op) { /* wrap around window */
206 from += wsize + write - op;
207 op -= write;
208 if (op < len) { /* some from end of window */
209 len -= op;
210 do {
211 PUP(out) = PUP(from);
212 } while (--op);
213 from = window - OFF;
214 if (write < len) { /* some from start of window */
215 op = write;
216 len -= op;
217 do {
218 PUP(out) = PUP(from);
219 } while (--op);
220 from = out - dist; /* rest from output */
221 }
222 }
223 }
224 else { /* contiguous in window */
225 from += write - op;
226 if (op < len) { /* some from window */
227 len -= op;
228 do {
229 PUP(out) = PUP(from);
230 } while (--op);
231 from = out - dist; /* rest from output */
232 }
233 }
234 while (len > 2) {
235 PUP(out) = PUP(from);
236 PUP(out) = PUP(from);
237 PUP(out) = PUP(from);
238 len -= 3;
239 }
240 if (len) {
241 PUP(out) = PUP(from);
242 if (len > 1)
243 PUP(out) = PUP(from);
244 }
245 }
246 else {
247 from = out - dist; /* copy direct from output */
248 do { /* minimum length is three */
249 PUP(out) = PUP(from);
250 PUP(out) = PUP(from);
251 PUP(out) = PUP(from);
252 len -= 3;
253 } while (len > 2);
254 if (len) {
255 PUP(out) = PUP(from);
256 if (len > 1)
257 PUP(out) = PUP(from);
258 }
259 }
260 }
261 else if ((op & 64) == 0) { /* 2nd level distance code */
262 this = dcode[this.val + (hold & ((1U << op) - 1))];
263 goto dodist;
264 }
265 else {
266 strm->msg = (char *)"invalid distance code";
267 state->mode = BAD;
268 break;
269 }
270 }
271 else if ((op & 64) == 0) { /* 2nd level length code */
272 this = lcode[this.val + (hold & ((1U << op) - 1))];
273 goto dolen;
274 }
275 else if (op & 32) { /* end-of-block */
276 Tracevv((stderr, "inflate: end of block\n"));
277 state->mode = TYPE;
278 break;
279 }
280 else {
281 strm->msg = (char *)"invalid literal/length code";
282 state->mode = BAD;
283 break;
284 }
285 } while (in < last && out < end);
286
287 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
288 len = bits >> 3;
289 in -= len;
290 bits -= len << 3;
291 hold &= (1U << bits) - 1;
292
293 /* update state and return */
294 strm->next_in = in + OFF;
295 strm->next_out = out + OFF;
296 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
297 strm->avail_out = (unsigned)(out < end ?
298 257 + (end - out) : 257 - (out - end));
299 state->hold = hold;
300 state->bits = bits;
301 return;
302 }
303
304 /*
305 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
306 - Using bit fields for code structure
307 - Different op definition to avoid & for extra bits (do & for table bits)
308 - Three separate decoding do-loops for direct, window, and write == 0
309 - Special case for distance > 1 copies to do overlapped load and store copy
310 - Explicit branch predictions (based on measured branch probabilities)
311 - Deferring match copy and interspersed it with decoding subsequent codes
312 - Swapping literal/length else
313 - Swapping window/direct else
314 - Larger unrolled copy loops (three is about right)
315 - Moving len -= 3 statement into middle of loop
316 */
317
318 #endif /* !ASMINF */