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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 { | |
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 */ | |
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 | ||
96 | void 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 | } | |
108 | ||
109 | av_cold void ff_lzw_decode_open(LZWState **p) | |
110 | { | |
111 | *p = av_mallocz(sizeof(struct LZWState)); | |
112 | } | |
113 | ||
114 | av_cold void ff_lzw_decode_close(LZWState **p) | |
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 | */ | |
165 | int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){ | |
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 | } |