FFmpeg coverage

Directory: ../../../ffmpeg/
File: src/libavcodec/lzw.c
Date: 2026-01-16 07:34:38
Exec Total Coverage
Lines: 91 98 92.9%
Functions: 6 6 100.0%
Branches: 37 48 77.1%
Line Branch Exec Source
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 "libavutil/attributes.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 2165926 static int lzw_get_code(struct LZWState * s)
71 {
72 int c;
73
74
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 2165926 if (s->bbits < s->cursize && bytestream2_get_bytes_left(&s->gb) <= 0)
75 ✗ return s->end_code;
76
77
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 2165926 if(s->mode == FF_LZW_GIF) {
78
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 5108593 while (s->bbits < s->cursize) {
79
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 2943050 if (!s->bs) {
80 12583 s->bs = bytestream2_get_byte(&s->gb);
81 }
82 2943050 s->bbuf |= bytestream2_get_byte(&s->gb) << s->bbits;
83 2943050 s->bbits += 8;
84 2943050 s->bs--;
85 }
86 2165543 c = s->bbuf;
87 2165543 s->bbuf >>= s->cursize;
88 } else { // TIFF
89
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 815 while (s->bbits < s->cursize) {
90 432 s->bbuf = (s->bbuf << 8) | bytestream2_get_byte(&s->gb);
91 432 s->bbits += 8;
92 }
93 383 c = s->bbuf >> (s->bbits - s->cursize);
94 }
95 2165926 s->bbits -= s->cursize;
96 2165926 return c & s->curmask;
97 }
98
99 1294 int ff_lzw_decode_tail(LZWState *p)
100 {
101 1294 struct LZWState *s = (struct LZWState *)p;
102
103
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 1294 if(s->mode == FF_LZW_GIF) {
104
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 2588 while (s->bs > 0 && bytestream2_get_bytes_left(&s->gb)) {
105 1294 bytestream2_skip(&s->gb, s->bs);
106 1294 s->bs = bytestream2_get_byte(&s->gb);
107 }
108 }else
109 ✗ bytestream2_skip(&s->gb, bytestream2_get_bytes_left(&s->gb));
110 1294 return bytestream2_tell(&s->gb);
111 }
112
113 57 av_cold void ff_lzw_decode_open(LZWState **p)
114 {
115 57 *p = av_mallocz(sizeof(struct LZWState));
116 57 }
117
118 57 av_cold void ff_lzw_decode_close(LZWState **p)
119 {
120 57 av_freep(p);
121 57 }
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 1296 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
132 {
133 1296 struct LZWState *s = (struct LZWState *)p;
134
135
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 1296 if(csize < 1 || csize >= LZW_MAXBITS)
136 ✗ return -1;
137 /* read buffer */
138 1296 bytestream2_init(&s->gb, buf, buf_size);
139 1296 s->bbuf = 0;
140 1296 s->bbits = 0;
141 1296 s->bs = 0;
142
143 /* decoder */
144 1296 s->codesize = csize;
145 1296 s->cursize = s->codesize + 1;
146 1296 s->curmask = mask[s->cursize];
147 1296 s->top_slot = 1 << s->cursize;
148 1296 s->clear_code = 1 << s->codesize;
149 1296 s->end_code = s->clear_code + 1;
150 1296 s->slot = s->newcodes = s->clear_code + 2;
151 1296 s->oc = s->fc = -1;
152 1296 s->sp = s->stack;
153
154 1296 s->mode = mode;
155 1296 s->extra_slot = s->mode == FF_LZW_TIFF;
156 1296 return 0;
157 }
158
159 /**
160 * Decode given number of bytes
161 * NOTE: the algorithm here is inspired from the LZW GIF decoder
162 * written by Steven A. Bennett in 1987.
163 *
164 * @param p LZW context
165 * @param buf output buffer
166 * @param len number of bytes to decode
167 * @return number of bytes decoded
168 */
169 37989 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
170 int l, c, code, oc, fc;
171 uint8_t *sp;
172 37989 struct LZWState *s = (struct LZWState *)p;
173
174
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 37989 if (s->end_code < 0)
175 ✗ return 0;
176
177 37989 l = len;
178 37989 sp = s->sp;
179 37989 oc = s->oc;
180 37989 fc = s->fc;
181
182 for (;;) {
183
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 7496317 while (sp > s->stack) {
184 5330391 *buf++ = *(--sp);
185
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 5330391 if ((--l) == 0)
186 37989 goto the_end;
187 }
188 2165926 c = lzw_get_code(s);
189
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 2165926 if (c == s->end_code) {
190 ✗ break;
191
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 2165926 } else if (c == s->clear_code) {
192 3062 s->cursize = s->codesize + 1;
193 3062 s->curmask = mask[s->cursize];
194 3062 s->slot = s->newcodes;
195 3062 s->top_slot = 1 << s->cursize;
196 3062 fc= oc= -1;
197 } else {
198 2162864 code = c;
199
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 2162864 if (code == s->slot && fc>=0) {
200 30234 *sp++ = fc;
201 30234 code = oc;
202
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 2132630 }else if(code >= s->slot)
203 ✗ break;
204
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 5300157 while (code >= s->newcodes) {
205 3137293 *sp++ = s->suffix[code];
206 3137293 code = s->prefix[code];
207 }
208 2162864 *sp++ = code;
209
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 2162864 if (s->slot < s->top_slot && oc>=0) {
210 2159802 s->suffix[s->slot] = code;
211 2159802 s->prefix[s->slot++] = oc;
212 }
213 2162864 fc = code;
214 2162864 oc = c;
215
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 2162864 if (s->slot >= s->top_slot - s->extra_slot) {
216
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 1563 if (s->cursize < LZW_MAXBITS) {
217 1563 s->top_slot <<= 1;
218 1563 s->curmask = mask[++s->cursize];
219 }
220 }
221 }
222 }
223 ✗ s->end_code = -1;
224 37989 the_end:
225 37989 s->sp = sp;
226 37989 s->oc = oc;
227 37989 s->fc = fc;
228 37989 return len - l;
229 }
230