aboutsummaryrefslogtreecommitdiffstats
path: root/libavcodec/lzw.c
blob: aa886910bea86f087974babbbbf4d5b105f6af18 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
/*
 * LZW decoder
 * Copyright (c) 2003 Fabrice Bellard
 * Copyright (c) 2006 Konstantin Shishkov
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * @brief LZW decoding routines
 * @author Fabrice Bellard
 * Modified for use in TIFF by Konstantin Shishkov
 */

#include "avcodec.h"
#include "lzw.h"

#define LZW_MAXBITS                 12
#define LZW_SIZTABLE                (1<<LZW_MAXBITS)

static const uint16_t mask[17] =
{
    0x0000, 0x0001, 0x0003, 0x0007,
    0x000F, 0x001F, 0x003F, 0x007F,
    0x00FF, 0x01FF, 0x03FF, 0x07FF,
    0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
};

struct LZWState {
    const uint8_t *pbuf, *ebuf;
    int bbits;
    unsigned int bbuf;

    int mode;                   ///< Decoder mode
    int cursize;                ///< The current code size
    int curmask;
    int codesize;
    int clear_code;
    int end_code;
    int newcodes;               ///< First available code
    int top_slot;               ///< Highest code for current size
    int extra_slot;
    int slot;                   ///< Last read code
    int fc, oc;
    uint8_t *sp;
    uint8_t stack[LZW_SIZTABLE];
    uint8_t suffix[LZW_SIZTABLE];
    uint16_t prefix[LZW_SIZTABLE];
    int bs;                     ///< current buffer size for GIF
};

/* get one code from stream */
static int lzw_get_code(struct LZWState * s)
{
    int c;

    if(s->mode == FF_LZW_GIF) {
        while (s->bbits < s->cursize) {
            if (!s->bs) {
                s->bs = *s->pbuf++;
            }
            s->bbuf |= (*s->pbuf++) << s->bbits;
            s->bbits += 8;
            s->bs--;
        }
        c = s->bbuf;
        s->bbuf >>= s->cursize;
    } else { // TIFF
        while (s->bbits < s->cursize) {
            s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
            s->bbits += 8;
        }
        c = s->bbuf >> (s->bbits - s->cursize);
    }
    s->bbits -= s->cursize;
    return c & s->curmask;
}

const uint8_t* ff_lzw_cur_ptr(LZWState *p)
{
    return ((struct LZWState*)p)->pbuf;
}

void ff_lzw_decode_tail(LZWState *p)
{
    struct LZWState *s = (struct LZWState *)p;

    if(s->mode == FF_LZW_GIF) {
        while(s->pbuf < s->ebuf && s->bs>0){
            s->pbuf += s->bs;
            s->bs = *s->pbuf++;
        }
    }else
        s->pbuf= s->ebuf;
}

av_cold void ff_lzw_decode_open(LZWState **p)
{
    *p = av_mallocz(sizeof(struct LZWState));
}

av_cold void ff_lzw_decode_close(LZWState **p)
{
    av_freep(p);
}

/**
 * Initialize LZW decoder
 * @param p LZW context
 * @param csize initial code size in bits
 * @param buf input data
 * @param buf_size input data size
 * @param mode decoder working mode - either GIF or TIFF
 */
int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
{
    struct LZWState *s = (struct LZWState *)p;

    if(csize < 1 || csize >= LZW_MAXBITS)
        return -1;
    /* read buffer */
    s->pbuf = buf;
    s->ebuf = s->pbuf + buf_size;
    s->bbuf = 0;
    s->bbits = 0;
    s->bs = 0;

    /* decoder */
    s->codesize = csize;
    s->cursize = s->codesize + 1;
    s->curmask = mask[s->cursize];
    s->top_slot = 1 << s->cursize;
    s->clear_code = 1 << s->codesize;
    s->end_code = s->clear_code + 1;
    s->slot = s->newcodes = s->clear_code + 2;
    s->oc = s->fc = -1;
    s->sp = s->stack;

    s->mode = mode;
    s->extra_slot = s->mode == FF_LZW_TIFF;
    return 0;
}

/**
 * Decode given number of bytes
 * NOTE: the algorithm here is inspired from the LZW GIF decoder
 *  written by Steven A. Bennett in 1987.
 *
 * @param p LZW context
 * @param buf output buffer
 * @param len number of bytes to decode
 * @return number of bytes decoded
 */
int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
    int l, c, code, oc, fc;
    uint8_t *sp;
    struct LZWState *s = (struct LZWState *)p;

    if (s->end_code < 0)
        return 0;

    l = len;
    sp = s->sp;
    oc = s->oc;
    fc = s->fc;

    for (;;) {
        while (sp > s->stack) {
            *buf++ = *(--sp);
            if ((--l) == 0)
                goto the_end;
        }
        c = lzw_get_code(s);
        if (c == s->end_code) {
            break;
        } else if (c == s->clear_code) {
            s->cursize = s->codesize + 1;
            s->curmask = mask[s->cursize];
            s->slot = s->newcodes;
            s->top_slot = 1 << s->cursize;
            fc= oc= -1;
        } else {
            code = c;
            if (code == s->slot && fc>=0) {
                *sp++ = fc;
                code = oc;
            }else if(code >= s->slot)
                break;
            while (code >= s->newcodes) {
                *sp++ = s->suffix[code];
                code = s->prefix[code];
            }
            *sp++ = code;
            if (s->slot < s->top_slot && oc>=0) {
                s->suffix[s->slot] = code;
                s->prefix[s->slot++] = oc;
            }
            fc = code;
            oc = c;
            if (s->slot >= s->top_slot - s->extra_slot) {
                if (s->cursize < LZW_MAXBITS) {
                    s->top_slot <<= 1;
                    s->curmask = mask[++s->cursize];
                }
            }
        }
    }
    s->end_code = -1;
  the_end:
    s->sp = sp;
    s->oc = oc;
    s->fc = fc;
    return len - l;
}