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(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
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