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 Libav.
7  *
8  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
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;
52  int cursize;
53  int curmask;
54  int codesize;
56  int end_code;
57  int newcodes;
58  int top_slot;
60  int slot;
61  int fc, oc;
65  uint16_t prefix[LZW_SIZTABLE];
66  int bs;
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 = p;
99  return bytestream2_tell(&s->gb);
100 }
101 
103 {
104  struct LZWState *s = (struct LZWState *)p;
105 
106  if(s->mode == FF_LZW_GIF) {
107  while (s->bs > 0 && bytestream2_get_bytes_left(&s->gb)) {
108  bytestream2_skip(&s->gb, s->bs);
109  s->bs = bytestream2_get_byte(&s->gb);
110  }
111  }else
113 }
114 
116 {
117  *p = av_mallocz(sizeof(struct LZWState));
118 }
119 
121 {
122  av_freep(p);
123 }
124 
133 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
134 {
135  struct LZWState *s = (struct LZWState *)p;
136 
137  if(csize < 1 || csize >= LZW_MAXBITS)
138  return -1;
139  /* read buffer */
140  bytestream2_init(&s->gb, buf, buf_size);
141  s->bbuf = 0;
142  s->bbits = 0;
143  s->bs = 0;
144 
145  /* decoder */
146  s->codesize = csize;
147  s->cursize = s->codesize + 1;
148  s->curmask = mask[s->cursize];
149  s->top_slot = 1 << s->cursize;
150  s->clear_code = 1 << s->codesize;
151  s->end_code = s->clear_code + 1;
152  s->slot = s->newcodes = s->clear_code + 2;
153  s->oc = s->fc = -1;
154  s->sp = s->stack;
155 
156  s->mode = mode;
157  s->extra_slot = s->mode == FF_LZW_TIFF;
158  return 0;
159 }
160 
171 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
172  int l, c, code, oc, fc;
173  uint8_t *sp;
174  struct LZWState *s = (struct LZWState *)p;
175 
176  if (s->end_code < 0)
177  return 0;
178 
179  l = len;
180  sp = s->sp;
181  oc = s->oc;
182  fc = s->fc;
183 
184  for (;;) {
185  while (sp > s->stack) {
186  *buf++ = *(--sp);
187  if ((--l) == 0)
188  goto the_end;
189  }
190  c = lzw_get_code(s);
191  if (c == s->end_code) {
192  break;
193  } else if (c == s->clear_code) {
194  s->cursize = s->codesize + 1;
195  s->curmask = mask[s->cursize];
196  s->slot = s->newcodes;
197  s->top_slot = 1 << s->cursize;
198  fc= oc= -1;
199  } else {
200  code = c;
201  if (code == s->slot && fc>=0) {
202  *sp++ = fc;
203  code = oc;
204  }else if(code >= s->slot)
205  break;
206  while (code >= s->newcodes) {
207  *sp++ = s->suffix[code];
208  code = s->prefix[code];
209  }
210  *sp++ = code;
211  if (s->slot < s->top_slot && oc>=0) {
212  s->suffix[s->slot] = code;
213  s->prefix[s->slot++] = oc;
214  }
215  fc = code;
216  oc = c;
217  if (s->slot >= s->top_slot - s->extra_slot) {
218  if (s->cursize < LZW_MAXBITS) {
219  s->top_slot <<= 1;
220  s->curmask = mask[++s->cursize];
221  }
222  }
223  }
224  }
225  s->end_code = -1;
226  the_end:
227  s->sp = sp;
228  s->oc = oc;
229  s->fc = fc;
230  return len - l;
231 }