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4f3865fb RP |
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 | |
1da177e4 LT |
4 | */ |
5 | ||
6 | #include <linux/zutil.h> | |
7 | #include "inftrees.h" | |
4f3865fb | 8 | #include "inflate.h" |
1da177e4 LT |
9 | #include "inffast.h" |
10 | ||
4f3865fb RP |
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. | |
b762450e RD |
66 | |
67 | - @start: inflate()'s starting value for strm->avail_out | |
4f3865fb | 68 | */ |
b762450e | 69 | void inflate_fast(z_streamp strm, unsigned start) |
1da177e4 | 70 | { |
4f3865fb | 71 | struct inflate_state *state; |
8336793b DV |
72 | const unsigned char *in; /* local strm->next_in */ |
73 | const unsigned char *last; /* while in < last, enough input available */ | |
74 | unsigned char *out; /* local strm->next_out */ | |
75 | unsigned char *beg; /* inflate()'s initial strm->next_out */ | |
76 | unsigned char *end; /* while out < end, enough space available */ | |
4f3865fb RP |
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 */ | |
8336793b | 83 | unsigned char *window; /* allocated sliding window, if wsize != 0 */ |
4f3865fb RP |
84 | unsigned long hold; /* local strm->hold */ |
85 | unsigned bits; /* local strm->bits */ | |
8336793b DV |
86 | code const *lcode; /* local strm->lencode */ |
87 | code const *dcode; /* local strm->distcode */ | |
4f3865fb RP |
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 */ | |
8336793b | 95 | unsigned char *from; /* where to copy match from */ |
4f3865fb RP |
96 | |
97 | /* copy state to local variables */ | |
98 | state = (struct inflate_state *)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 */ | |
1da177e4 | 120 | do { |
4f3865fb RP |
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 | PUP(out) = (unsigned char)(this.val); | |
135 | } | |
136 | else if (op & 16) { /* length base */ | |
137 | len = (unsigned)(this.val); | |
138 | op &= 15; /* number of extra bits */ | |
139 | if (op) { | |
140 | if (bits < op) { | |
141 | hold += (unsigned long)(PUP(in)) << bits; | |
142 | bits += 8; | |
143 | } | |
144 | len += (unsigned)hold & ((1U << op) - 1); | |
145 | hold >>= op; | |
146 | bits -= op; | |
147 | } | |
148 | if (bits < 15) { | |
149 | hold += (unsigned long)(PUP(in)) << bits; | |
150 | bits += 8; | |
151 | hold += (unsigned long)(PUP(in)) << bits; | |
152 | bits += 8; | |
153 | } | |
154 | this = dcode[hold & dmask]; | |
155 | dodist: | |
156 | op = (unsigned)(this.bits); | |
157 | hold >>= op; | |
158 | bits -= op; | |
159 | op = (unsigned)(this.op); | |
160 | if (op & 16) { /* distance base */ | |
161 | dist = (unsigned)(this.val); | |
162 | op &= 15; /* number of extra bits */ | |
163 | if (bits < op) { | |
164 | hold += (unsigned long)(PUP(in)) << bits; | |
165 | bits += 8; | |
166 | if (bits < op) { | |
167 | hold += (unsigned long)(PUP(in)) << bits; | |
168 | bits += 8; | |
169 | } | |
170 | } | |
171 | dist += (unsigned)hold & ((1U << op) - 1); | |
172 | #ifdef INFLATE_STRICT | |
173 | if (dist > dmax) { | |
174 | strm->msg = (char *)"invalid distance too far back"; | |
175 | state->mode = BAD; | |
176 | break; | |
177 | } | |
178 | #endif | |
179 | hold >>= op; | |
180 | bits -= op; | |
181 | op = (unsigned)(out - beg); /* max distance in output */ | |
182 | if (dist > op) { /* see if copy from window */ | |
183 | op = dist - op; /* distance back in window */ | |
184 | if (op > whave) { | |
185 | strm->msg = (char *)"invalid distance too far back"; | |
186 | state->mode = BAD; | |
187 | break; | |
188 | } | |
189 | from = window - OFF; | |
190 | if (write == 0) { /* very common case */ | |
191 | from += wsize - op; | |
192 | if (op < len) { /* some from window */ | |
193 | len -= op; | |
194 | do { | |
195 | PUP(out) = PUP(from); | |
196 | } while (--op); | |
197 | from = out - dist; /* rest from output */ | |
198 | } | |
199 | } | |
200 | else if (write < op) { /* wrap around window */ | |
201 | from += wsize + write - op; | |
202 | op -= write; | |
203 | if (op < len) { /* some from end of window */ | |
204 | len -= op; | |
205 | do { | |
206 | PUP(out) = PUP(from); | |
207 | } while (--op); | |
208 | from = window - OFF; | |
209 | if (write < len) { /* some from start of window */ | |
210 | op = write; | |
211 | len -= op; | |
212 | do { | |
213 | PUP(out) = PUP(from); | |
214 | } while (--op); | |
215 | from = out - dist; /* rest from output */ | |
216 | } | |
217 | } | |
218 | } | |
219 | else { /* contiguous in window */ | |
220 | from += write - op; | |
221 | if (op < len) { /* some from window */ | |
222 | len -= op; | |
223 | do { | |
224 | PUP(out) = PUP(from); | |
225 | } while (--op); | |
226 | from = out - dist; /* rest from output */ | |
227 | } | |
228 | } | |
229 | while (len > 2) { | |
230 | PUP(out) = PUP(from); | |
231 | PUP(out) = PUP(from); | |
232 | PUP(out) = PUP(from); | |
233 | len -= 3; | |
234 | } | |
235 | if (len) { | |
236 | PUP(out) = PUP(from); | |
237 | if (len > 1) | |
238 | PUP(out) = PUP(from); | |
239 | } | |
240 | } | |
241 | else { | |
242 | from = out - dist; /* copy direct from output */ | |
243 | do { /* minimum length is three */ | |
244 | PUP(out) = PUP(from); | |
245 | PUP(out) = PUP(from); | |
246 | PUP(out) = PUP(from); | |
247 | len -= 3; | |
248 | } while (len > 2); | |
249 | if (len) { | |
250 | PUP(out) = PUP(from); | |
251 | if (len > 1) | |
252 | PUP(out) = PUP(from); | |
253 | } | |
254 | } | |
255 | } | |
256 | else if ((op & 64) == 0) { /* 2nd level distance code */ | |
257 | this = dcode[this.val + (hold & ((1U << op) - 1))]; | |
258 | goto dodist; | |
1da177e4 | 259 | } |
4f3865fb RP |
260 | else { |
261 | strm->msg = (char *)"invalid distance code"; | |
262 | state->mode = BAD; | |
263 | break; | |
1da177e4 | 264 | } |
4f3865fb RP |
265 | } |
266 | else if ((op & 64) == 0) { /* 2nd level length code */ | |
267 | this = lcode[this.val + (hold & ((1U << op) - 1))]; | |
268 | goto dolen; | |
269 | } | |
270 | else if (op & 32) { /* end-of-block */ | |
271 | state->mode = TYPE; | |
1da177e4 | 272 | break; |
1da177e4 | 273 | } |
4f3865fb RP |
274 | else { |
275 | strm->msg = (char *)"invalid literal/length code"; | |
276 | state->mode = BAD; | |
277 | break; | |
278 | } | |
279 | } while (in < last && out < end); | |
280 | ||
281 | /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ | |
282 | len = bits >> 3; | |
283 | in -= len; | |
284 | bits -= len << 3; | |
285 | hold &= (1U << bits) - 1; | |
286 | ||
287 | /* update state and return */ | |
288 | strm->next_in = in + OFF; | |
289 | strm->next_out = out + OFF; | |
290 | strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); | |
291 | strm->avail_out = (unsigned)(out < end ? | |
292 | 257 + (end - out) : 257 - (out - end)); | |
293 | state->hold = hold; | |
294 | state->bits = bits; | |
295 | return; | |
1da177e4 | 296 | } |
4f3865fb RP |
297 | |
298 | /* | |
299 | inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): | |
300 | - Using bit fields for code structure | |
301 | - Different op definition to avoid & for extra bits (do & for table bits) | |
302 | - Three separate decoding do-loops for direct, window, and write == 0 | |
303 | - Special case for distance > 1 copies to do overlapped load and store copy | |
304 | - Explicit branch predictions (based on measured branch probabilities) | |
305 | - Deferring match copy and interspersed it with decoding subsequent codes | |
306 | - Swapping literal/length else | |
307 | - Swapping window/direct else | |
308 | - Larger unrolled copy loops (three is about right) | |
309 | - Moving len -= 3 statement into middle of loop | |
310 | */ | |
311 | ||
312 | #endif /* !ASMINF */ |