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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 "bytestream.h"
32 #include "lzw.h"
33 #include "libavutil/mem.h"
34 
35 #define LZW_MAXBITS 12
36 #define LZW_SIZTABLE (1<<LZW_MAXBITS)
37 
38 static const uint16_t mask[17] =
39 {
40  0x0000, 0x0001, 0x0003, 0x0007,
41  0x000F, 0x001F, 0x003F, 0x007F,
42  0x00FF, 0x01FF, 0x03FF, 0x07FF,
43  0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
44 };
45 
46 struct LZWState {
48  int bbits;
49  unsigned int bbuf;
50 
51  int mode; ///< Decoder mode
52  int cursize; ///< The current code size
53  int curmask;
54  int codesize;
56  int end_code;
57  int newcodes; ///< First available code
58  int top_slot; ///< Highest code for current size
60  int slot; ///< Last read code
61  int fc, oc;
65  uint16_t prefix[LZW_SIZTABLE];
66  int bs; ///< current buffer size for GIF
67 };
68 
69 /* get one code from stream */
70 static int lzw_get_code(struct LZWState * s)
71 {
72  int c;
73 
74  if(s->mode == FF_LZW_GIF) {
75  while (s->bbits < s->cursize) {
76  if (!s->bs) {
77  s->bs = bytestream2_get_byte(&s->gb);
78  }
79  s->bbuf |= bytestream2_get_byte(&s->gb) << s->bbits;
80  s->bbits += 8;
81  s->bs--;
82  }
83  c = s->bbuf;
84  s->bbuf >>= s->cursize;
85  } else { // TIFF
86  while (s->bbits < s->cursize) {
87  s->bbuf = (s->bbuf << 8) | bytestream2_get_byte(&s->gb);
88  s->bbits += 8;
89  }
90  c = s->bbuf >> (s->bbits - s->cursize);
91  }
92  s->bbits -= s->cursize;
93  return c & s->curmask;
94 }
95 
97 {
98  struct LZWState *s = (struct LZWState *)p;
99 
100  if(s->mode == FF_LZW_GIF) {
101  while (s->bs > 0 && bytestream2_get_bytes_left(&s->gb)) {
102  bytestream2_skip(&s->gb, s->bs);
103  s->bs = bytestream2_get_byte(&s->gb);
104  }
105  }else
107 }
108 
110 {
111  *p = av_mallocz(sizeof(struct LZWState));
112 }
113 
115 {
116  av_freep(p);
117 }
118 
119 /**
120  * Initialize LZW decoder
121  * @param p LZW context
122  * @param csize initial code size in bits
123  * @param buf input data
124  * @param buf_size input data size
125  * @param mode decoder working mode - either GIF or TIFF
126  */
127 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
128 {
129  struct LZWState *s = (struct LZWState *)p;
130 
131  if(csize < 1 || csize >= LZW_MAXBITS)
132  return -1;
133  /* read buffer */
134  bytestream2_init(&s->gb, buf, buf_size);
135  s->bbuf = 0;
136  s->bbits = 0;
137  s->bs = 0;
138 
139  /* decoder */
140  s->codesize = csize;
141  s->cursize = s->codesize + 1;
142  s->curmask = mask[s->cursize];
143  s->top_slot = 1 << s->cursize;
144  s->clear_code = 1 << s->codesize;
145  s->end_code = s->clear_code + 1;
146  s->slot = s->newcodes = s->clear_code + 2;
147  s->oc = s->fc = -1;
148  s->sp = s->stack;
149 
150  s->mode = mode;
151  s->extra_slot = s->mode == FF_LZW_TIFF;
152  return 0;
153 }
154 
155 /**
156  * Decode given number of bytes
157  * NOTE: the algorithm here is inspired from the LZW GIF decoder
158  * written by Steven A. Bennett in 1987.
159  *
160  * @param p LZW context
161  * @param buf output buffer
162  * @param len number of bytes to decode
163  * @return number of bytes decoded
164  */
166  int l, c, code, oc, fc;
167  uint8_t *sp;
168  struct LZWState *s = (struct LZWState *)p;
169 
170  if (s->end_code < 0)
171  return 0;
172 
173  l = len;
174  sp = s->sp;
175  oc = s->oc;
176  fc = s->fc;
177 
178  for (;;) {
179  while (sp > s->stack) {
180  *buf++ = *(--sp);
181  if ((--l) == 0)
182  goto the_end;
183  }
184  c = lzw_get_code(s);
185  if (c == s->end_code) {
186  break;
187  } else if (c == s->clear_code) {
188  s->cursize = s->codesize + 1;
189  s->curmask = mask[s->cursize];
190  s->slot = s->newcodes;
191  s->top_slot = 1 << s->cursize;
192  fc= oc= -1;
193  } else {
194  code = c;
195  if (code == s->slot && fc>=0) {
196  *sp++ = fc;
197  code = oc;
198  }else if(code >= s->slot)
199  break;
200  while (code >= s->newcodes) {
201  *sp++ = s->suffix[code];
202  code = s->prefix[code];
203  }
204  *sp++ = code;
205  if (s->slot < s->top_slot && oc>=0) {
206  s->suffix[s->slot] = code;
207  s->prefix[s->slot++] = oc;
208  }
209  fc = code;
210  oc = c;
211  if (s->slot >= s->top_slot - s->extra_slot) {
212  if (s->cursize < LZW_MAXBITS) {
213  s->top_slot <<= 1;
214  s->curmask = mask[++s->cursize];
215  }
216  }
217  }
218  }
219  s->end_code = -1;
220  the_end:
221  s->sp = sp;
222  s->oc = oc;
223  s->fc = fc;
224  return len - l;
225 }