Statistics
| Branch: | Revision:

ffmpeg / libavcodec / bitstream.c @ 676d380f

History | View | Annotate | Download (10.3 KB)

1
/*
2
 * Common bit i/o utils
3
 * Copyright (c) 2000, 2001 Fabrice Bellard
4
 * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
5
 * Copyright (c) 2010 Loren Merritt
6
 *
7
 * alternative bitstream reader & writer by Michael Niedermayer <michaelni@gmx.at>
8
 *
9
 * This file is part of FFmpeg.
10
 *
11
 * FFmpeg is free software; you can redistribute it and/or
12
 * modify it under the terms of the GNU Lesser General Public
13
 * License as published by the Free Software Foundation; either
14
 * version 2.1 of the License, or (at your option) any later version.
15
 *
16
 * FFmpeg is distributed in the hope that it will be useful,
17
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
19
 * Lesser General Public License for more details.
20
 *
21
 * You should have received a copy of the GNU Lesser General Public
22
 * License along with FFmpeg; if not, write to the Free Software
23
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24
 */
25

    
26
/**
27
 * @file
28
 * bitstream api.
29
 */
30

    
31
#include "avcodec.h"
32
#include "get_bits.h"
33
#include "put_bits.h"
34

    
35
const uint8_t ff_log2_run[41]={
36
 0, 0, 0, 0, 1, 1, 1, 1,
37
 2, 2, 2, 2, 3, 3, 3, 3,
38
 4, 4, 5, 5, 6, 6, 7, 7,
39
 8, 9,10,11,12,13,14,15,
40
16,17,18,19,20,21,22,23,
41
24,
42
};
43

    
44
void align_put_bits(PutBitContext *s)
45
{
46
#ifdef ALT_BITSTREAM_WRITER
47
    put_bits(s,(  - s->index) & 7,0);
48
#else
49
    put_bits(s,s->bit_left & 7,0);
50
#endif
51
}
52

    
53
void ff_put_string(PutBitContext *pb, const char *string, int terminate_string)
54
{
55
    while(*string){
56
        put_bits(pb, 8, *string);
57
        string++;
58
    }
59
    if(terminate_string)
60
        put_bits(pb, 8, 0);
61
}
62

    
63
void ff_copy_bits(PutBitContext *pb, const uint8_t *src, int length)
64
{
65
    int words= length>>4;
66
    int bits= length&15;
67
    int i;
68

    
69
    if(length==0) return;
70

    
71
    if(CONFIG_SMALL || words < 16 || put_bits_count(pb)&7){
72
        for(i=0; i<words; i++) put_bits(pb, 16, AV_RB16(src + 2*i));
73
    }else{
74
        for(i=0; put_bits_count(pb)&31; i++)
75
            put_bits(pb, 8, src[i]);
76
        flush_put_bits(pb);
77
        memcpy(put_bits_ptr(pb), src+i, 2*words-i);
78
        skip_put_bytes(pb, 2*words-i);
79
    }
80

    
81
    put_bits(pb, bits, AV_RB16(src + 2*words)>>(16-bits));
82
}
83

    
84
/* VLC decoding */
85

    
86
//#define DEBUG_VLC
87

    
88
#define GET_DATA(v, table, i, wrap, size) \
89
{\
90
    const uint8_t *ptr = (const uint8_t *)table + i * wrap;\
91
    switch(size) {\
92
    case 1:\
93
        v = *(const uint8_t *)ptr;\
94
        break;\
95
    case 2:\
96
        v = *(const uint16_t *)ptr;\
97
        break;\
98
    default:\
99
        v = *(const uint32_t *)ptr;\
100
        break;\
101
    }\
102
}
103

    
104

    
105
static int alloc_table(VLC *vlc, int size, int use_static)
106
{
107
    int index;
108
    index = vlc->table_size;
109
    vlc->table_size += size;
110
    if (vlc->table_size > vlc->table_allocated) {
111
        if(use_static)
112
            abort(); //cant do anything, init_vlc() is used with too little memory
113
        vlc->table_allocated += (1 << vlc->bits);
114
        vlc->table = av_realloc(vlc->table,
115
                                sizeof(VLC_TYPE) * 2 * vlc->table_allocated);
116
        if (!vlc->table)
117
            return -1;
118
    }
119
    return index;
120
}
121

    
122
static av_always_inline uint32_t bitswap_32(uint32_t x) {
123
    return av_reverse[x&0xFF]<<24
124
         | av_reverse[(x>>8)&0xFF]<<16
125
         | av_reverse[(x>>16)&0xFF]<<8
126
         | av_reverse[x>>24];
127
}
128

    
129
typedef struct {
130
    uint8_t bits;
131
    uint16_t symbol;
132
    /** codeword, with the first bit-to-be-read in the msb
133
     * (even if intended for a little-endian bitstream reader) */
134
    uint32_t code;
135
} VLCcode;
136

    
137
static int compare_vlcspec(const void *a, const void *b)
138
{
139
    const VLCcode *sa=a, *sb=b;
140
    return (sa->code >> 1) - (sb->code >> 1);
141
}
142

    
143
/**
144
 * Build VLC decoding tables suitable for use with get_vlc().
145
 *
146
 * @param vlc            the context to be initted
147
 *
148
 * @param table_nb_bits  max length of vlc codes to store directly in this table
149
 *                       (Longer codes are delegated to subtables.)
150
 *
151
 * @param nb_codes       number of elements in codes[]
152
 *
153
 * @param codes          descriptions of the vlc codes
154
 *                       These must be ordered such that codes going into the same subtable are contiguous.
155
 *                       Sorting by VLCcode.code is sufficient, though not necessary.
156
 */
157
static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,
158
                       VLCcode *codes, int flags)
159
{
160
    int table_size, table_index, index, code_prefix, symbol, subtable_bits;
161
    int i, j, k, n, nb, inc;
162
    uint32_t code;
163
    VLC_TYPE (*table)[2];
164

    
165
    table_size = 1 << table_nb_bits;
166
    table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);
167
#ifdef DEBUG_VLC
168
    av_log(NULL,AV_LOG_DEBUG,"new table index=%d size=%d\n",
169
           table_index, table_size);
170
#endif
171
    if (table_index < 0)
172
        return -1;
173
    table = &vlc->table[table_index];
174

    
175
    for (i = 0; i < table_size; i++) {
176
        table[i][1] = 0; //bits
177
        table[i][0] = -1; //codes
178
    }
179

    
180
    /* first pass: map codes and compute auxillary table sizes */
181
    for (i = 0; i < nb_codes; i++) {
182
        n = codes[i].bits;
183
        code = codes[i].code;
184
        symbol = codes[i].symbol;
185
#if defined(DEBUG_VLC) && 0
186
        av_log(NULL,AV_LOG_DEBUG,"i=%d n=%d code=0x%x\n", i, n, code);
187
#endif
188
        if (n <= table_nb_bits) {
189
            /* no need to add another table */
190
            j = code >> (32 - table_nb_bits);
191
            nb = 1 << (table_nb_bits - n);
192
            inc = 1;
193
            if (flags & INIT_VLC_LE) {
194
                j = bitswap_32(code);
195
                inc = 1 << n;
196
            }
197
            for (k = 0; k < nb; k++) {
198
#ifdef DEBUG_VLC
199
                av_log(NULL, AV_LOG_DEBUG, "%4x: code=%d n=%d\n",
200
                       j, i, n);
201
#endif
202
                if (table[j][1] /*bits*/ != 0) {
203
                    av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");
204
                    return -1;
205
                }
206
                table[j][1] = n; //bits
207
                table[j][0] = symbol;
208
                j += inc;
209
            }
210
        } else {
211
            /* fill auxiliary table recursively */
212
            n -= table_nb_bits;
213
            code_prefix = code >> (32 - table_nb_bits);
214
            subtable_bits = n;
215
            codes[i].bits = n;
216
            codes[i].code = code << table_nb_bits;
217
            for (k = i+1; k < nb_codes; k++) {
218
                n = codes[k].bits - table_nb_bits;
219
                if (n <= 0)
220
                    break;
221
                code = codes[k].code;
222
                if (code >> (32 - table_nb_bits) != code_prefix)
223
                    break;
224
                codes[k].bits = n;
225
                codes[k].code = code << table_nb_bits;
226
                subtable_bits = FFMAX(subtable_bits, n);
227
            }
228
            subtable_bits = FFMIN(subtable_bits, table_nb_bits);
229
            j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;
230
            table[j][1] = -subtable_bits;
231
#ifdef DEBUG_VLC
232
            av_log(NULL,AV_LOG_DEBUG,"%4x: n=%d (subtable)\n",
233
                   j, codes[i].bits + table_nb_bits);
234
#endif
235
            index = build_table(vlc, subtable_bits, k-i, codes+i, flags);
236
            if (index < 0)
237
                return -1;
238
            /* note: realloc has been done, so reload tables */
239
            table = &vlc->table[table_index];
240
            table[j][0] = index; //code
241
            i = k-1;
242
        }
243
    }
244
    return table_index;
245
}
246

    
247

    
248
/* Build VLC decoding tables suitable for use with get_vlc().
249

250
   'nb_bits' set thee decoding table size (2^nb_bits) entries. The
251
   bigger it is, the faster is the decoding. But it should not be too
252
   big to save memory and L1 cache. '9' is a good compromise.
253

254
   'nb_codes' : number of vlcs codes
255

256
   'bits' : table which gives the size (in bits) of each vlc code.
257

258
   'codes' : table which gives the bit pattern of of each vlc code.
259

260
   'symbols' : table which gives the values to be returned from get_vlc().
261

262
   'xxx_wrap' : give the number of bytes between each entry of the
263
   'bits' or 'codes' tables.
264

265
   'xxx_size' : gives the number of bytes of each entry of the 'bits'
266
   or 'codes' tables.
267

268
   'wrap' and 'size' allows to use any memory configuration and types
269
   (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.
270

271
   'use_static' should be set to 1 for tables, which should be freed
272
   with av_free_static(), 0 if free_vlc() will be used.
273
*/
274
int init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
275
             const void *bits, int bits_wrap, int bits_size,
276
             const void *codes, int codes_wrap, int codes_size,
277
             const void *symbols, int symbols_wrap, int symbols_size,
278
             int flags)
279
{
280
    VLCcode *buf;
281
    int i, j, ret;
282

    
283
    vlc->bits = nb_bits;
284
    if(flags & INIT_VLC_USE_NEW_STATIC){
285
        if(vlc->table_size && vlc->table_size == vlc->table_allocated){
286
            return 0;
287
        }else if(vlc->table_size){
288
            abort(); // fatal error, we are called on a partially initialized table
289
        }
290
    }else {
291
        vlc->table = NULL;
292
        vlc->table_allocated = 0;
293
        vlc->table_size = 0;
294
    }
295

    
296
#ifdef DEBUG_VLC
297
    av_log(NULL,AV_LOG_DEBUG,"build table nb_codes=%d\n", nb_codes);
298
#endif
299

    
300
    buf = av_malloc((nb_codes+1)*sizeof(VLCcode));
301

    
302
    assert(symbols_size <= 2 || !symbols);
303
    j = 0;
304
#define COPY(condition)\
305
    for (i = 0; i < nb_codes; i++) {\
306
        GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size);\
307
        if (!(condition))\
308
            continue;\
309
        GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size);\
310
        if (flags & INIT_VLC_LE)\
311
            buf[j].code = bitswap_32(buf[j].code);\
312
        else\
313
            buf[j].code <<= 32 - buf[j].bits;\
314
        if (symbols)\
315
            GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size)\
316
        else\
317
            buf[j].symbol = i;\
318
        j++;\
319
    }
320
    COPY(buf[j].bits > nb_bits);
321
    // qsort is the slowest part of init_vlc, and could probably be improved or avoided
322
    qsort(buf, j, sizeof(VLCcode), compare_vlcspec);
323
    COPY(buf[j].bits && buf[j].bits <= nb_bits);
324
    nb_codes = j;
325

    
326
    ret = build_table(vlc, nb_bits, nb_codes, buf, flags);
327

    
328
    av_free(buf);
329
    if (ret < 0) {
330
        av_freep(&vlc->table);
331
        return -1;
332
    }
333
    if((flags & INIT_VLC_USE_NEW_STATIC) && vlc->table_size != vlc->table_allocated)
334
        av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);
335
    return 0;
336
}
337

    
338

    
339
void free_vlc(VLC *vlc)
340
{
341
    av_freep(&vlc->table);
342
}
343