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comparison mupdf-source/thirdparty/zlib/inffast.c @ 2:b50eed0cc0ef upstream

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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1:1d09e1dec1d9 2:b50eed0cc0ef
1 /* inffast.c -- fast decoding
2 * Copyright (C) 1995-2017 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 #ifdef ASMINF
12 # pragma message("Assembler code may have bugs -- use at your own risk")
13 #else
14
15 /*
16 Decode literal, length, and distance codes and write out the resulting
17 literal and match bytes until either not enough input or output is
18 available, an end-of-block is encountered, or a data error is encountered.
19 When large enough input and output buffers are supplied to inflate(), for
20 example, a 16K input buffer and a 64K output buffer, more than 95% of the
21 inflate execution time is spent in this routine.
22
23 Entry assumptions:
24
25 state->mode == LEN
26 strm->avail_in >= 6
27 strm->avail_out >= 258
28 start >= strm->avail_out
29 state->bits < 8
30
31 On return, state->mode is one of:
32
33 LEN -- ran out of enough output space or enough available input
34 TYPE -- reached end of block code, inflate() to interpret next block
35 BAD -- error in block data
36
37 Notes:
38
39 - The maximum input bits used by a length/distance pair is 15 bits for the
40 length code, 5 bits for the length extra, 15 bits for the distance code,
41 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
42 Therefore if strm->avail_in >= 6, then there is enough input to avoid
43 checking for available input while decoding.
44
45 - The maximum bytes that a single length/distance pair can output is 258
46 bytes, which is the maximum length that can be coded. inflate_fast()
47 requires strm->avail_out >= 258 for each loop to avoid checking for
48 output space.
49 */
50 void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
51 struct inflate_state FAR *state;
52 z_const unsigned char FAR *in; /* local strm->next_in */
53 z_const unsigned char FAR *last; /* have enough input while in < last */
54 unsigned char FAR *out; /* local strm->next_out */
55 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
56 unsigned char FAR *end; /* while out < end, enough space available */
57 #ifdef INFLATE_STRICT
58 unsigned dmax; /* maximum distance from zlib header */
59 #endif
60 unsigned wsize; /* window size or zero if not using window */
61 unsigned whave; /* valid bytes in the window */
62 unsigned wnext; /* window write index */
63 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
64 unsigned long hold; /* local strm->hold */
65 unsigned bits; /* local strm->bits */
66 code const FAR *lcode; /* local strm->lencode */
67 code const FAR *dcode; /* local strm->distcode */
68 unsigned lmask; /* mask for first level of length codes */
69 unsigned dmask; /* mask for first level of distance codes */
70 code const *here; /* retrieved table entry */
71 unsigned op; /* code bits, operation, extra bits, or */
72 /* window position, window bytes to copy */
73 unsigned len; /* match length, unused bytes */
74 unsigned dist; /* match distance */
75 unsigned char FAR *from; /* where to copy match from */
76
77 /* copy state to local variables */
78 state = (struct inflate_state FAR *)strm->state;
79 in = strm->next_in;
80 last = in + (strm->avail_in - 5);
81 out = strm->next_out;
82 beg = out - (start - strm->avail_out);
83 end = out + (strm->avail_out - 257);
84 #ifdef INFLATE_STRICT
85 dmax = state->dmax;
86 #endif
87 wsize = state->wsize;
88 whave = state->whave;
89 wnext = state->wnext;
90 window = state->window;
91 hold = state->hold;
92 bits = state->bits;
93 lcode = state->lencode;
94 dcode = state->distcode;
95 lmask = (1U << state->lenbits) - 1;
96 dmask = (1U << state->distbits) - 1;
97
98 /* decode literals and length/distances until end-of-block or not enough
99 input data or output space */
100 do {
101 if (bits < 15) {
102 hold += (unsigned long)(*in++) << bits;
103 bits += 8;
104 hold += (unsigned long)(*in++) << bits;
105 bits += 8;
106 }
107 here = lcode + (hold & lmask);
108 dolen:
109 op = (unsigned)(here->bits);
110 hold >>= op;
111 bits -= op;
112 op = (unsigned)(here->op);
113 if (op == 0) { /* literal */
114 Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ?
115 "inflate: literal '%c'\n" :
116 "inflate: literal 0x%02x\n", here->val));
117 *out++ = (unsigned char)(here->val);
118 }
119 else if (op & 16) { /* length base */
120 len = (unsigned)(here->val);
121 op &= 15; /* number of extra bits */
122 if (op) {
123 if (bits < op) {
124 hold += (unsigned long)(*in++) << bits;
125 bits += 8;
126 }
127 len += (unsigned)hold & ((1U << op) - 1);
128 hold >>= op;
129 bits -= op;
130 }
131 Tracevv((stderr, "inflate: length %u\n", len));
132 if (bits < 15) {
133 hold += (unsigned long)(*in++) << bits;
134 bits += 8;
135 hold += (unsigned long)(*in++) << bits;
136 bits += 8;
137 }
138 here = dcode + (hold & dmask);
139 dodist:
140 op = (unsigned)(here->bits);
141 hold >>= op;
142 bits -= op;
143 op = (unsigned)(here->op);
144 if (op & 16) { /* distance base */
145 dist = (unsigned)(here->val);
146 op &= 15; /* number of extra bits */
147 if (bits < op) {
148 hold += (unsigned long)(*in++) << bits;
149 bits += 8;
150 if (bits < op) {
151 hold += (unsigned long)(*in++) << bits;
152 bits += 8;
153 }
154 }
155 dist += (unsigned)hold & ((1U << op) - 1);
156 #ifdef INFLATE_STRICT
157 if (dist > dmax) {
158 strm->msg = (char *)"invalid distance too far back";
159 state->mode = BAD;
160 break;
161 }
162 #endif
163 hold >>= op;
164 bits -= op;
165 Tracevv((stderr, "inflate: distance %u\n", dist));
166 op = (unsigned)(out - beg); /* max distance in output */
167 if (dist > op) { /* see if copy from window */
168 op = dist - op; /* distance back in window */
169 if (op > whave) {
170 if (state->sane) {
171 strm->msg =
172 (char *)"invalid distance too far back";
173 state->mode = BAD;
174 break;
175 }
176 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
177 if (len <= op - whave) {
178 do {
179 *out++ = 0;
180 } while (--len);
181 continue;
182 }
183 len -= op - whave;
184 do {
185 *out++ = 0;
186 } while (--op > whave);
187 if (op == 0) {
188 from = out - dist;
189 do {
190 *out++ = *from++;
191 } while (--len);
192 continue;
193 }
194 #endif
195 }
196 from = window;
197 if (wnext == 0) { /* very common case */
198 from += wsize - op;
199 if (op < len) { /* some from window */
200 len -= op;
201 do {
202 *out++ = *from++;
203 } while (--op);
204 from = out - dist; /* rest from output */
205 }
206 }
207 else if (wnext < op) { /* wrap around window */
208 from += wsize + wnext - op;
209 op -= wnext;
210 if (op < len) { /* some from end of window */
211 len -= op;
212 do {
213 *out++ = *from++;
214 } while (--op);
215 from = window;
216 if (wnext < len) { /* some from start of window */
217 op = wnext;
218 len -= op;
219 do {
220 *out++ = *from++;
221 } while (--op);
222 from = out - dist; /* rest from output */
223 }
224 }
225 }
226 else { /* contiguous in window */
227 from += wnext - op;
228 if (op < len) { /* some from window */
229 len -= op;
230 do {
231 *out++ = *from++;
232 } while (--op);
233 from = out - dist; /* rest from output */
234 }
235 }
236 while (len > 2) {
237 *out++ = *from++;
238 *out++ = *from++;
239 *out++ = *from++;
240 len -= 3;
241 }
242 if (len) {
243 *out++ = *from++;
244 if (len > 1)
245 *out++ = *from++;
246 }
247 }
248 else {
249 from = out - dist; /* copy direct from output */
250 do { /* minimum length is three */
251 *out++ = *from++;
252 *out++ = *from++;
253 *out++ = *from++;
254 len -= 3;
255 } while (len > 2);
256 if (len) {
257 *out++ = *from++;
258 if (len > 1)
259 *out++ = *from++;
260 }
261 }
262 }
263 else if ((op & 64) == 0) { /* 2nd level distance code */
264 here = dcode + here->val + (hold & ((1U << op) - 1));
265 goto dodist;
266 }
267 else {
268 strm->msg = (char *)"invalid distance code";
269 state->mode = BAD;
270 break;
271 }
272 }
273 else if ((op & 64) == 0) { /* 2nd level length code */
274 here = lcode + here->val + (hold & ((1U << op) - 1));
275 goto dolen;
276 }
277 else if (op & 32) { /* end-of-block */
278 Tracevv((stderr, "inflate: end of block\n"));
279 state->mode = TYPE;
280 break;
281 }
282 else {
283 strm->msg = (char *)"invalid literal/length code";
284 state->mode = BAD;
285 break;
286 }
287 } while (in < last && out < end);
288
289 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
290 len = bits >> 3;
291 in -= len;
292 bits -= len << 3;
293 hold &= (1U << bits) - 1;
294
295 /* update state and return */
296 strm->next_in = in;
297 strm->next_out = out;
298 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
299 strm->avail_out = (unsigned)(out < end ?
300 257 + (end - out) : 257 - (out - end));
301 state->hold = hold;
302 state->bits = bits;
303 return;
304 }
305
306 /*
307 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
308 - Using bit fields for code structure
309 - Different op definition to avoid & for extra bits (do & for table bits)
310 - Three separate decoding do-loops for direct, window, and wnext == 0
311 - Special case for distance > 1 copies to do overlapped load and store copy
312 - Explicit branch predictions (based on measured branch probabilities)
313 - Deferring match copy and interspersed it with decoding subsequent codes
314 - Swapping literal/length else
315 - Swapping window/direct else
316 - Larger unrolled copy loops (three is about right)
317 - Moving len -= 3 statement into middle of loop
318 */
319
320 #endif /* !ASMINF */