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lzw.c
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1 /*
2  * LZW decoder
3  * Copyright (c) 2003 Fabrice Bellard
4  * Copyright (c) 2006 Konstantin Shishkov
5  *
6  * This file is part of FFmpeg.
7  *
8  * FFmpeg is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * FFmpeg is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with FFmpeg; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 /**
24  * @file
25  * @brief LZW decoding routines
26  * @author Fabrice Bellard
27  * @author modified for use in TIFF by Konstantin Shishkov
28  */
29 
30 #include "avcodec.h"
31 #include "lzw.h"
32 #include "libavutil/mem.h"
33 
34 #define LZW_MAXBITS 12
35 #define LZW_SIZTABLE (1<<LZW_MAXBITS)
36 
37 static const uint16_t mask[17] =
38 {
39  0x0000, 0x0001, 0x0003, 0x0007,
40  0x000F, 0x001F, 0x003F, 0x007F,
41  0x00FF, 0x01FF, 0x03FF, 0x07FF,
42  0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
43 };
44 
45 struct LZWState {
46  const uint8_t *pbuf, *ebuf;
47  int bbits;
48  unsigned int bbuf;
49 
50  int mode; ///< Decoder mode
51  int cursize; ///< The current code size
52  int curmask;
53  int codesize;
55  int end_code;
56  int newcodes; ///< First available code
57  int top_slot; ///< Highest code for current size
59  int slot; ///< Last read code
60  int fc, oc;
64  uint16_t prefix[LZW_SIZTABLE];
65  int bs; ///< current buffer size for GIF
66 };
67 
68 /* get one code from stream */
69 static int lzw_get_code(struct LZWState * s)
70 {
71  int c;
72 
73  if(s->mode == FF_LZW_GIF) {
74  while (s->bbits < s->cursize) {
75  if (!s->bs) {
76  s->bs = *s->pbuf++;
77  }
78  s->bbuf |= (*s->pbuf++) << s->bbits;
79  s->bbits += 8;
80  s->bs--;
81  }
82  c = s->bbuf;
83  s->bbuf >>= s->cursize;
84  } else { // TIFF
85  while (s->bbits < s->cursize) {
86  s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
87  s->bbits += 8;
88  }
89  c = s->bbuf >> (s->bbits - s->cursize);
90  }
91  s->bbits -= s->cursize;
92  return c & s->curmask;
93 }
94 
96 {
97  struct LZWState *s = (struct LZWState *)p;
98 
99  if(s->mode == FF_LZW_GIF) {
100  while (s->bs > 0) {
101  if (s->bs >= s->ebuf - s->pbuf) {
102  s->pbuf = s->ebuf;
103  break;
104  } else {
105  s->pbuf += s->bs;
106  s->bs = *s->pbuf++;
107  }
108  }
109  }else
110  s->pbuf= s->ebuf;
111 }
112 
114 {
115  *p = av_mallocz(sizeof(struct LZWState));
116 }
117 
119 {
120  av_freep(p);
121 }
122 
123 /**
124  * Initialize LZW decoder
125  * @param p LZW context
126  * @param csize initial code size in bits
127  * @param buf input data
128  * @param buf_size input data size
129  * @param mode decoder working mode - either GIF or TIFF
130  */
131 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
132 {
133  struct LZWState *s = (struct LZWState *)p;
134 
135  if(csize < 1 || csize >= LZW_MAXBITS)
136  return -1;
137  /* read buffer */
138  s->pbuf = buf;
139  s->ebuf = s->pbuf + buf_size;
140  s->bbuf = 0;
141  s->bbits = 0;
142  s->bs = 0;
143 
144  /* decoder */
145  s->codesize = csize;
146  s->cursize = s->codesize + 1;
147  s->curmask = mask[s->cursize];
148  s->top_slot = 1 << s->cursize;
149  s->clear_code = 1 << s->codesize;
150  s->end_code = s->clear_code + 1;
151  s->slot = s->newcodes = s->clear_code + 2;
152  s->oc = s->fc = -1;
153  s->sp = s->stack;
154 
155  s->mode = mode;
156  s->extra_slot = s->mode == FF_LZW_TIFF;
157  return 0;
158 }
159 
160 /**
161  * Decode given number of bytes
162  * NOTE: the algorithm here is inspired from the LZW GIF decoder
163  * written by Steven A. Bennett in 1987.
164  *
165  * @param p LZW context
166  * @param buf output buffer
167  * @param len number of bytes to decode
168  * @return number of bytes decoded
169  */
171  int l, c, code, oc, fc;
172  uint8_t *sp;
173  struct LZWState *s = (struct LZWState *)p;
174 
175  if (s->end_code < 0)
176  return 0;
177 
178  l = len;
179  sp = s->sp;
180  oc = s->oc;
181  fc = s->fc;
182 
183  for (;;) {
184  while (sp > s->stack) {
185  *buf++ = *(--sp);
186  if ((--l) == 0)
187  goto the_end;
188  }
189  if (s->ebuf < s->pbuf) {
190  av_log(NULL, AV_LOG_ERROR, "lzw overread\n");
191  goto the_end;
192  }
193  c = lzw_get_code(s);
194  if (c == s->end_code) {
195  break;
196  } else if (c == s->clear_code) {
197  s->cursize = s->codesize + 1;
198  s->curmask = mask[s->cursize];
199  s->slot = s->newcodes;
200  s->top_slot = 1 << s->cursize;
201  fc= oc= -1;
202  } else {
203  code = c;
204  if (code == s->slot && fc>=0) {
205  *sp++ = fc;
206  code = oc;
207  }else if(code >= s->slot)
208  break;
209  while (code >= s->newcodes) {
210  *sp++ = s->suffix[code];
211  code = s->prefix[code];
212  }
213  *sp++ = code;
214  if (s->slot < s->top_slot && oc>=0) {
215  s->suffix[s->slot] = code;
216  s->prefix[s->slot++] = oc;
217  }
218  fc = code;
219  oc = c;
220  if (s->slot >= s->top_slot - s->extra_slot) {
221  if (s->cursize < LZW_MAXBITS) {
222  s->top_slot <<= 1;
223  s->curmask = mask[++s->cursize];
224  }
225  }
226  }
227  }
228  s->end_code = -1;
229  the_end:
230  s->sp = sp;
231  s->oc = oc;
232  s->fc = fc;
233  return len - l;
234 }