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