FFmpeg: libavcodec/bitstream.c Source File

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libavcodec

bitstream.c

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1 /*

2 * Common bit i/o utils

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 */

26 /**

27 * @file

28 * bitstream api.

29 */

31 #include "libavutil/atomic.h"

32 #include "libavutil/avassert.h"

33 #include "avcodec.h"

34 #include "mathops.h"

35 #include "get_bits.h"

36 #include "put_bits.h"

38 const uint8_t ff_log2_run[41]={

39 0, 0, 0, 0, 1, 1, 1, 1,

40 2, 2, 2, 2, 3, 3, 3, 3,

41 4, 4, 5, 5, 6, 6, 7, 7,

42 8, 9,10,11,12,13,14,15,

43 16,17,18,19,20,21,22,23,

44 24,

45 };

47 void avpriv_align_put_bits(PutBitContext *s)

48 {

49 put_bits(s, s->bit_left & 7, 0);

50 }

52 void avpriv_put_string(PutBitContext *pb, const char *string,

53 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 }

63 void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length)

64 {

65 int words = length >> 4;

66 int bits = length & 15;

67 int i;

69 if (length == 0)

70 return;

72 if (CONFIG_SMALL || words < 16 || put_bits_count(pb) & 7) {

73 for (i = 0; i < words; i++)

74 put_bits(pb, 16, AV_RB16(src + 2 * i));

75 } else {

76 for (i = 0; put_bits_count(pb) & 31; i++)

77 put_bits(pb, 8, src[i]);

78 flush_put_bits(pb);

79 memcpy(put_bits_ptr(pb), src + i, 2 * words - i);

80 skip_put_bytes(pb, 2 * words - i);

81 }

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

84 }

86 /* VLC decoding */

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 = vlc->table_size;

108

109 vlc->table_size += size;

110 if (vlc->table_size > vlc->table_allocated) {

111 if (use_static)

112 abort(); // cannot do anything, init_vlc() is used with too little memory

113 vlc->table_allocated += (1 << vlc->bits);

114 vlc->table = av_realloc_f(vlc->table, vlc->table_allocated, sizeof(VLC_TYPE) * 2);

115 if (!vlc->table) {

116 vlc->table_allocated = 0;

117 vlc->table_size = 0;

118 return AVERROR(ENOMEM);

119 }

120 memset(vlc->table + vlc->table_allocated - (1 << vlc->bits), 0, sizeof(VLC_TYPE) * 2 << vlc->bits);

121 }

122 return index;

123 }

124

125 static av_always_inline uint32_t bitswap_32(uint32_t x)

126 {

127 return (uint32_t)ff_reverse[ x & 0xFF] << 24 |

128 (uint32_t)ff_reverse[(x >> 8) & 0xFF] << 16 |

129 (uint32_t)ff_reverse[(x >> 16) & 0xFF] << 8 |

130 (uint32_t)ff_reverse[ x >> 24];

131 }

132

133 typedef struct {

134 uint8_t bits;

135 uint16_t symbol;

136 /** codeword, with the first bit-to-be-read in the msb

137 * (even if intended for a little-endian bitstream reader) */

138 uint32_t code;

139 } VLCcode;

140

141 static int compare_vlcspec(const void *a, const void *b)

142 {

143 const VLCcode *sa = a, *sb = b;

144 return (sa->code >> 1) - (sb->code >> 1);

145 }

146 /**

147 * Build VLC decoding tables suitable for use with get_vlc().

148 *

149 * @param vlc the context to be initted

150 *

151 * @param table_nb_bits max length of vlc codes to store directly in this table

152 * (Longer codes are delegated to subtables.)

153 *

154 * @param nb_codes number of elements in codes[]

155 *

156 * @param codes descriptions of the vlc codes

157 * These must be ordered such that codes going into the same subtable are contiguous.

158 * Sorting by VLCcode.code is sufficient, though not necessary.

159 */

160 static int build_table(VLC *vlc, int table_nb_bits, int nb_codes,

161 VLCcode *codes, int flags)

162 {

163 int table_size, table_index, index, code_prefix, symbol, subtable_bits;

164 int i, j, k, n, nb, inc;

165 uint32_t code;

166 volatile VLC_TYPE (* volatile table)[2]; // the double volatile is needed to prevent a internal compiler error in gcc 4.2

167

168 table_size = 1 << table_nb_bits;

169 if (table_nb_bits > 30)

170 return -1;

171 table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_NEW_STATIC);

172 av_dlog(NULL, "new table index=%d size=%d\n", table_index, table_size);

173 if (table_index < 0)

174 return table_index;

175 table = (volatile VLC_TYPE (*)[2])&vlc->table[table_index];

176

177 /* first pass: map codes and compute auxiliary table sizes */

178 for (i = 0; i < nb_codes; i++) {

179 n = codes[i].bits;

180 code = codes[i].code;

181 symbol = codes[i].symbol;

182 av_dlog(NULL, "i=%d n=%d code=0x%x\n", i, n, code);

183 if (n <= table_nb_bits) {

184 /* no need to add another table */

185 j = code >> (32 - table_nb_bits);

186 nb = 1 << (table_nb_bits - n);

187 inc = 1;

188 if (flags & INIT_VLC_LE) {

189 j = bitswap_32(code);

190 inc = 1 << n;

191 }

192 for (k = 0; k < nb; k++) {

193 int bits = table[j][1];

194 av_dlog(NULL, "%4x: code=%d n=%d\n", j, i, n);

195 if (bits != 0 && bits != n) {

196 av_log(NULL, AV_LOG_ERROR, "incorrect codes\n");

197 return AVERROR_INVALIDDATA;

198 }

199 table[j][1] = n; //bits

200 table[j][0] = symbol;

201 j += inc;

202 }

203 } else {

204 /* fill auxiliary table recursively */

205 n -= table_nb_bits;

206 code_prefix = code >> (32 - table_nb_bits);

207 subtable_bits = n;

208 codes[i].bits = n;

209 codes[i].code = code << table_nb_bits;

210 for (k = i+1; k < nb_codes; k++) {

211 n = codes[k].bits - table_nb_bits;

212 if (n <= 0)

213 break;

214 code = codes[k].code;

215 if (code >> (32 - table_nb_bits) != code_prefix)

216 break;

217 codes[k].bits = n;

218 codes[k].code = code << table_nb_bits;

219 subtable_bits = FFMAX(subtable_bits, n);

220 }

221 subtable_bits = FFMIN(subtable_bits, table_nb_bits);

222 j = (flags & INIT_VLC_LE) ? bitswap_32(code_prefix) >> (32 - table_nb_bits) : code_prefix;

223 table[j][1] = -subtable_bits;

224 av_dlog(NULL, "%4x: n=%d (subtable)\n",

225 j, codes[i].bits + table_nb_bits);

226 index = build_table(vlc, subtable_bits, k-i, codes+i, flags);

227 if (index < 0)

228 return index;

229 /* note: realloc has been done, so reload tables */

230 table = (volatile VLC_TYPE (*)[2])&vlc->table[table_index];

231 table[j][0] = index; //code

232 i = k-1;

233 }

234 }

235

236 for (i = 0; i < table_size; i++) {

237 if (table[i][1] == 0) //bits

238 table[i][0] = -1; //codes

239 }

240

241 return table_index;

242 }

243

244

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

246

247 'nb_bits' set thee decoding table size (2^nb_bits) entries. The

248 bigger it is, the faster is the decoding. But it should not be too

249 big to save memory and L1 cache. '9' is a good compromise.

250

251 'nb_codes' : number of vlcs codes

252

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

254

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

256

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

258

259 'xxx_wrap' : give the number of bytes between each entry of the

260 'bits' or 'codes' tables.

261

262 'xxx_size' : gives the number of bytes of each entry of the 'bits'

263 or 'codes' tables.

264

265 'wrap' and 'size' allows to use any memory configuration and types

266 (byte/word/long) to store the 'bits', 'codes', and 'symbols' tables.

267

268 'use_static' should be set to 1 for tables, which should be freed

269 with av_free_static(), 0 if ff_free_vlc() will be used.

270 */

271 int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes,

272 const void *bits, int bits_wrap, int bits_size,

273 const void *codes, int codes_wrap, int codes_size,

274 const void *symbols, int symbols_wrap, int symbols_size,

275 int flags)

276 {

277 VLCcode *buf;

278 int i, j, ret;

279 VLCcode localbuf[1500]; // the maximum currently needed is 1296 by rv34

280 VLC localvlc, *vlc;

281

282 vlc = vlc_arg;

283 vlc->bits = nb_bits;

284 if (flags & INIT_VLC_USE_NEW_STATIC) {

285 av_assert0(nb_codes + 1 <= FF_ARRAY_ELEMS(localbuf));

286 buf = localbuf;

287 localvlc = *vlc_arg;

288 vlc = &localvlc;

289 vlc->table_size = 0;

290 } else {

291 vlc->table = NULL;

292 vlc->table_allocated = 0;

293 vlc->table_size = 0;

294

295 buf = av_malloc_array((nb_codes + 1), sizeof(VLCcode));

296 if (!buf)

297 return AVERROR(ENOMEM);

298 }

299

300

301 av_assert0(symbols_size <= 2 || !symbols);

302 j = 0;

303 #define COPY(condition)\

304 for (i = 0; i < nb_codes; i++) { \

305 GET_DATA(buf[j].bits, bits, i, bits_wrap, bits_size); \

306 if (!(condition)) \

307 continue; \

308 if (buf[j].bits > 3*nb_bits || buf[j].bits>32) { \

309 av_log(NULL, AV_LOG_ERROR, "Too long VLC (%d) in init_vlc\n", buf[j].bits);\

310 if (!(flags & INIT_VLC_USE_NEW_STATIC)) \

311 av_free(buf); \

312 return -1; \

313 } \

314 GET_DATA(buf[j].code, codes, i, codes_wrap, codes_size); \

315 if (buf[j].code >= (1LL<<buf[j].bits)) { \

316 av_log(NULL, AV_LOG_ERROR, "Invalid code in init_vlc\n"); \

317 if (!(flags & INIT_VLC_USE_NEW_STATIC)) \

318 av_free(buf); \

319 return -1; \

320 } \

321 if (flags & INIT_VLC_LE) \

322 buf[j].code = bitswap_32(buf[j].code); \

323 else \

324 buf[j].code <<= 32 - buf[j].bits; \

325 if (symbols) \

326 GET_DATA(buf[j].symbol, symbols, i, symbols_wrap, symbols_size) \

327 else \

328 buf[j].symbol = i; \

329 j++; \

330 }

331 COPY(buf[j].bits > nb_bits);

332 // qsort is the slowest part of init_vlc, and could probably be improved or avoided

333 qsort(buf, j, sizeof(VLCcode), compare_vlcspec);

334 COPY(buf[j].bits && buf[j].bits <= nb_bits);

335 nb_codes = j;

336

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

338

339 if (flags & INIT_VLC_USE_NEW_STATIC) {

340 if(vlc->table_size != vlc->table_allocated)

341 av_log(NULL, AV_LOG_ERROR, "needed %d had %d\n", vlc->table_size, vlc->table_allocated);

342

343 av_assert0(ret >= 0);

344 *vlc_arg = *vlc;

345 } else {

346 av_free(buf);

347 if (ret < 0) {

348 av_freep(&vlc->table);

349 return ret;

350 }

351 }

352 return 0;

353 }

354

355

356 void ff_free_vlc(VLC *vlc)

357 {

358 av_freep(&vlc->table);

359 }

Generated on Sun Jul 20 2014 23:05:44 for FFmpeg by doxygen 1.8.2