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path: root/libavcodec/lzw.c (plain)
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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
38static 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
46struct LZWState {
47 GetByteContext gb;
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;
55 int clear_code;
56 int end_code;
57 int newcodes; ///< First available code
58 int top_slot; ///< Highest code for current size
59 int extra_slot;
60 int slot; ///< Last read code
61 int fc, oc;
62 uint8_t *sp;
63 uint8_t stack[LZW_SIZTABLE];
64 uint8_t suffix[LZW_SIZTABLE];
65 uint16_t prefix[LZW_SIZTABLE];
66 int bs; ///< current buffer size for GIF
67};
68
69/* get one code from stream */
70static 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
96int ff_lzw_decode_tail(LZWState *p)
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
106 bytestream2_skip(&s->gb, bytestream2_get_bytes_left(&s->gb));
107 return bytestream2_tell(&s->gb);
108}
109
110av_cold void ff_lzw_decode_open(LZWState **p)
111{
112 *p = av_mallocz(sizeof(struct LZWState));
113}
114
115av_cold void ff_lzw_decode_close(LZWState **p)
116{
117 av_freep(p);
118}
119
120/**
121 * Initialize LZW decoder
122 * @param p LZW context
123 * @param csize initial code size in bits
124 * @param buf input data
125 * @param buf_size input data size
126 * @param mode decoder working mode - either GIF or TIFF
127 */
128int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
129{
130 struct LZWState *s = (struct LZWState *)p;
131
132 if(csize < 1 || csize >= LZW_MAXBITS)
133 return -1;
134 /* read buffer */
135 bytestream2_init(&s->gb, buf, buf_size);
136 s->bbuf = 0;
137 s->bbits = 0;
138 s->bs = 0;
139
140 /* decoder */
141 s->codesize = csize;
142 s->cursize = s->codesize + 1;
143 s->curmask = mask[s->cursize];
144 s->top_slot = 1 << s->cursize;
145 s->clear_code = 1 << s->codesize;
146 s->end_code = s->clear_code + 1;
147 s->slot = s->newcodes = s->clear_code + 2;
148 s->oc = s->fc = -1;
149 s->sp = s->stack;
150
151 s->mode = mode;
152 s->extra_slot = s->mode == FF_LZW_TIFF;
153 return 0;
154}
155
156/**
157 * Decode given number of bytes
158 * NOTE: the algorithm here is inspired from the LZW GIF decoder
159 * written by Steven A. Bennett in 1987.
160 *
161 * @param p LZW context
162 * @param buf output buffer
163 * @param len number of bytes to decode
164 * @return number of bytes decoded
165 */
166int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
167 int l, c, code, oc, fc;
168 uint8_t *sp;
169 struct LZWState *s = (struct LZWState *)p;
170
171 if (s->end_code < 0)
172 return 0;
173
174 l = len;
175 sp = s->sp;
176 oc = s->oc;
177 fc = s->fc;
178
179 for (;;) {
180 while (sp > s->stack) {
181 *buf++ = *(--sp);
182 if ((--l) == 0)
183 goto the_end;
184 }
185 c = lzw_get_code(s);
186 if (c == s->end_code) {
187 break;
188 } else if (c == s->clear_code) {
189 s->cursize = s->codesize + 1;
190 s->curmask = mask[s->cursize];
191 s->slot = s->newcodes;
192 s->top_slot = 1 << s->cursize;
193 fc= oc= -1;
194 } else {
195 code = c;
196 if (code == s->slot && fc>=0) {
197 *sp++ = fc;
198 code = oc;
199 }else if(code >= s->slot)
200 break;
201 while (code >= s->newcodes) {
202 *sp++ = s->suffix[code];
203 code = s->prefix[code];
204 }
205 *sp++ = code;
206 if (s->slot < s->top_slot && oc>=0) {
207 s->suffix[s->slot] = code;
208 s->prefix[s->slot++] = oc;
209 }
210 fc = code;
211 oc = c;
212 if (s->slot >= s->top_slot - s->extra_slot) {
213 if (s->cursize < LZW_MAXBITS) {
214 s->top_slot <<= 1;
215 s->curmask = mask[++s->cursize];
216 }
217 }
218 }
219 }
220 s->end_code = -1;
221 the_end:
222 s->sp = sp;
223 s->oc = oc;
224 s->fc = fc;
225 return len - l;
226}
227
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