inffast.c
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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 */
inflate_state
Definition: inflate.h:77
state
state
PUP
#define PUP(a)
Definition: inffast.c:29
inflate_state::wsize
unsigned wsize
Definition: inflate.h:89
inflate_state::distbits
unsigned distbits
Definition: inflate.h:105
inflate_state::distcode
code const FAR * distcode
Definition: inflate.h:103
inflate_state::last
int last
Definition: inflate.h:79
TYPE
Definition: inflate.h:32
OFF
#define OFF
Definition: inffast.c:28
inflate_state::lenbits
unsigned lenbits
Definition: inflate.h:104
inflate_state::hold
unsigned long hold
Definition: inflate.h:94
val
int val
Definition: jpeglib.h:956
inflate_state::write
unsigned write
Definition: inflate.h:91
start
png_size_t start
Definition: png.h:1496
code
Definition: inftrees.h:24
inflate_state::dmax
unsigned dmax
Definition: inflate.h:83
inflate_state::bits
unsigned bits
Definition: inflate.h:95
inflate_state::window
unsigned char FAR * window
Definition: inflate.h:92
inflate_state::mode
inflate_mode mode
Definition: inflate.h:78
BAD
Definition: inflate.h:48
inflate_fast
void inflate_fast(z_streamp strm, unsigned start)
Definition: inffast.c:67
inflate_state::whave
unsigned whave
Definition: inflate.h:90
z_streamp
z_stream FAR * z_streamp
Definition: zlib.h:103
inflate_state::lencode
code const FAR * lencode
Definition: inflate.h:102
Tracevv
#define Tracevv(x)
Definition: zutil.h:255

openhrp3
Author(s): AIST, General Robotix Inc., Nakamura Lab of Dept. of Mechano Informatics at University of Tokyo
autogenerated on Thu Sep 8 2022 02:24:03