3 * Copyright (c) 2003 Fabrice Bellard
4 * Copyright (c) 2006 Konstantin Shishkov
6 * This file is part of FFmpeg.
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.
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.
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
25 * @brief LZW decoding routines
26 * @author Fabrice Bellard
27 * @author modified for use in TIFF by Konstantin Shishkov
33 #define LZW_MAXBITS 12
34 #define LZW_SIZTABLE (1<<LZW_MAXBITS)
36 static const uint16_t mask[17] =
38 0x0000, 0x0001, 0x0003, 0x0007,
39 0x000F, 0x001F, 0x003F, 0x007F,
40 0x00FF, 0x01FF, 0x03FF, 0x07FF,
41 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
45 const uint8_t *pbuf, *ebuf;
49 int mode; ///< Decoder mode
50 int cursize; ///< The current code size
55 int newcodes; ///< First available code
56 int top_slot; ///< Highest code for current size
58 int slot; ///< Last read code
61 uint8_t stack[LZW_SIZTABLE];
62 uint8_t suffix[LZW_SIZTABLE];
63 uint16_t prefix[LZW_SIZTABLE];
64 int bs; ///< current buffer size for GIF
67 /* get one code from stream */
68 static int lzw_get_code(struct LZWState * s)
72 if(s->mode == FF_LZW_GIF) {
73 while (s->bbits < s->cursize) {
77 s->bbuf |= (*s->pbuf++) << s->bbits;
82 s->bbuf >>= s->cursize;
84 while (s->bbits < s->cursize) {
85 s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
88 c = s->bbuf >> (s->bbits - s->cursize);
90 s->bbits -= s->cursize;
91 return c & s->curmask;
94 const uint8_t* ff_lzw_cur_ptr(LZWState *p)
96 return ((struct LZWState*)p)->pbuf;
99 void ff_lzw_decode_tail(LZWState *p)
101 struct LZWState *s = (struct LZWState *)p;
103 if(s->mode == FF_LZW_GIF) {
105 if (s->bs >= s->ebuf - s->pbuf) {
117 av_cold void ff_lzw_decode_open(LZWState **p)
119 *p = av_mallocz(sizeof(struct LZWState));
122 av_cold void ff_lzw_decode_close(LZWState **p)
128 * Initialize LZW decoder
129 * @param p LZW context
130 * @param csize initial code size in bits
131 * @param buf input data
132 * @param buf_size input data size
133 * @param mode decoder working mode - either GIF or TIFF
135 int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
137 struct LZWState *s = (struct LZWState *)p;
139 if(csize < 1 || csize >= LZW_MAXBITS)
143 s->ebuf = s->pbuf + buf_size;
150 s->cursize = s->codesize + 1;
151 s->curmask = mask[s->cursize];
152 s->top_slot = 1 << s->cursize;
153 s->clear_code = 1 << s->codesize;
154 s->end_code = s->clear_code + 1;
155 s->slot = s->newcodes = s->clear_code + 2;
160 s->extra_slot = s->mode == FF_LZW_TIFF;
165 * Decode given number of bytes
166 * NOTE: the algorithm here is inspired from the LZW GIF decoder
167 * written by Steven A. Bennett in 1987.
169 * @param p LZW context
170 * @param buf output buffer
171 * @param len number of bytes to decode
172 * @return number of bytes decoded
174 int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
175 int l, c, code, oc, fc;
177 struct LZWState *s = (struct LZWState *)p;
188 while (sp > s->stack) {
194 if (c == s->end_code) {
196 } else if (c == s->clear_code) {
197 s->cursize = s->codesize + 1;
198 s->curmask = mask[s->cursize];
199 s->slot = s->newcodes;
200 s->top_slot = 1 << s->cursize;
204 if (code == s->slot && fc>=0) {
207 }else if(code >= s->slot)
209 while (code >= s->newcodes) {
210 *sp++ = s->suffix[code];
211 code = s->prefix[code];
214 if (s->slot < s->top_slot && oc>=0) {
215 s->suffix[s->slot] = code;
216 s->prefix[s->slot++] = oc;
220 if (s->slot >= s->top_slot - s->extra_slot) {
221 if (s->cursize < LZW_MAXBITS) {
223 s->curmask = mask[++s->cursize];