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 libavcodec/lzw.c
25 * @brief LZW decoding routines
26 * @author Fabrice Bellard
27 * Modified for use in TIFF by Konstantin Shishkov
28 */
29
30#include "avcodec.h"
31#include "lzw.h"
32
33#define LZW_MAXBITS                 12
34#define LZW_SIZTABLE                (1<<LZW_MAXBITS)
35
36static const uint16_t mask[17] =
37{
38    0x0000, 0x0001, 0x0003, 0x0007,
39    0x000F, 0x001F, 0x003F, 0x007F,
40    0x00FF, 0x01FF, 0x03FF, 0x07FF,
41    0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
42};
43
44struct LZWState {
45    const uint8_t *pbuf, *ebuf;
46    int bbits;
47    unsigned int bbuf;
48
49    int mode;                   ///< Decoder mode
50    int cursize;                ///< The current code size
51    int curmask;
52    int codesize;
53    int clear_code;
54    int end_code;
55    int newcodes;               ///< First available code
56    int top_slot;               ///< Highest code for current size
57    int extra_slot;
58    int slot;                   ///< Last read code
59    int fc, oc;
60    uint8_t *sp;
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
65};
66
67/* get one code from stream */
68static int lzw_get_code(struct LZWState * s)
69{
70    int c;
71
72    if(s->mode == FF_LZW_GIF) {
73        while (s->bbits < s->cursize) {
74            if (!s->bs) {
75                s->bs = *s->pbuf++;
76            }
77            s->bbuf |= (*s->pbuf++) << s->bbits;
78            s->bbits += 8;
79            s->bs--;
80        }
81        c = s->bbuf;
82        s->bbuf >>= s->cursize;
83    } else { // TIFF
84        while (s->bbits < s->cursize) {
85            s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
86            s->bbits += 8;
87        }
88        c = s->bbuf >> (s->bbits - s->cursize);
89    }
90    s->bbits -= s->cursize;
91    return c & s->curmask;
92}
93
94const uint8_t* ff_lzw_cur_ptr(LZWState *p)
95{
96    return ((struct LZWState*)p)->pbuf;
97}
98
99void ff_lzw_decode_tail(LZWState *p)
100{
101    struct LZWState *s = (struct LZWState *)p;
102
103    if(s->mode == FF_LZW_GIF) {
104        while(s->pbuf < s->ebuf && s->bs>0){
105            s->pbuf += s->bs;
106            s->bs = *s->pbuf++;
107        }
108    }else
109        s->pbuf= s->ebuf;
110}
111
112av_cold void ff_lzw_decode_open(LZWState **p)
113{
114    *p = av_mallocz(sizeof(struct LZWState));
115}
116
117av_cold void ff_lzw_decode_close(LZWState **p)
118{
119    av_freep(p);
120}
121
122/**
123 * Initialize LZW decoder
124 * @param s LZW context
125 * @param csize initial code size in bits
126 * @param buf input data
127 * @param buf_size input data size
128 * @param mode decoder working mode - either GIF or TIFF
129 */
130int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
131{
132    struct LZWState *s = (struct LZWState *)p;
133
134    if(csize < 1 || csize >= LZW_MAXBITS)
135        return -1;
136    /* read buffer */
137    s->pbuf = buf;
138    s->ebuf = s->pbuf + buf_size;
139    s->bbuf = 0;
140    s->bbits = 0;
141    s->bs = 0;
142
143    /* decoder */
144    s->codesize = csize;
145    s->cursize = s->codesize + 1;
146    s->curmask = mask[s->cursize];
147    s->top_slot = 1 << s->cursize;
148    s->clear_code = 1 << s->codesize;
149    s->end_code = s->clear_code + 1;
150    s->slot = s->newcodes = s->clear_code + 2;
151    s->oc = s->fc = -1;
152    s->sp = s->stack;
153
154    s->mode = mode;
155    s->extra_slot = s->mode == FF_LZW_TIFF;
156    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 s LZW context
165 * @param buf output buffer
166 * @param len number of bytes to decode
167 * @return number of bytes decoded
168 */
169int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
170    int l, c, code, oc, fc;
171    uint8_t *sp;
172    struct LZWState *s = (struct LZWState *)p;
173
174    if (s->end_code < 0)
175        return 0;
176
177    l = len;
178    sp = s->sp;
179    oc = s->oc;
180    fc = s->fc;
181
182    for (;;) {
183        while (sp > s->stack) {
184            *buf++ = *(--sp);
185            if ((--l) == 0)
186                goto the_end;
187        }
188        c = lzw_get_code(s);
189        if (c == s->end_code) {
190            break;
191        } else if (c == s->clear_code) {
192            s->cursize = s->codesize + 1;
193            s->curmask = mask[s->cursize];
194            s->slot = s->newcodes;
195            s->top_slot = 1 << s->cursize;
196            fc= oc= -1;
197        } else {
198            code = c;
199            if (code == s->slot && fc>=0) {
200                *sp++ = fc;
201                code = oc;
202            }else if(code >= s->slot)
203                break;
204            while (code >= s->newcodes) {
205                *sp++ = s->suffix[code];
206                code = s->prefix[code];
207            }
208            *sp++ = code;
209            if (s->slot < s->top_slot && oc>=0) {
210                s->suffix[s->slot] = code;
211                s->prefix[s->slot++] = oc;
212            }
213            fc = code;
214            oc = c;
215            if (s->slot >= s->top_slot - s->extra_slot) {
216                if (s->cursize < LZW_MAXBITS) {
217                    s->top_slot <<= 1;
218                    s->curmask = mask[++s->cursize];
219                }
220            }
221        }
222    }
223    s->end_code = -1;
224  the_end:
225    s->sp = sp;
226    s->oc = oc;
227    s->fc = fc;
228    return len - l;
229}
230