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/avassert.h"

32 #include "avcodec.h"

33 #include "mathops.h"

34 #include "get_bits.h"

35 #include "put_bits.h"

37 const uint8_t ff_log2_run[41]={

38 0, 0, 0, 0, 1, 1, 1, 1,

39 2, 2, 2, 2, 3, 3, 3, 3,

40 4, 4, 5, 5, 6, 6, 7, 7,

41 8, 9,10,11,12,13,14,15,

42 16,17,18,19,20,21,22,23,

43 24,

44 };

46 void avpriv_align_put_bits(PutBitContext *s)

47 {

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

49 }

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

52 int terminate_string)

53 {

54 while (*string) {

55 put_bits(pb, 8, *string);

56 string++;

57 }

58 if (terminate_string)

59 put_bits(pb, 8, 0);

60 }

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

63 {

64 int words = length >> 4;

65 int bits = length & 15;

66 int i;

68 if (length == 0)

69 return;

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

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

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

74 } else {

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

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

77 flush_put_bits(pb);

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

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

80 }

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

83 }

85 /* VLC decoding */

87 #define GET_DATA(v, table, i, wrap, size) \

88 { \

89 const uint8_t *ptr = (const uint8_t *)table + i * wrap; \

90 switch(size) { \

91 case 1: \

92 v = *(const uint8_t *)ptr; \

93 break; \

94 case 2: \

95 v = *(const uint16_t *)ptr; \

96 break; \

97 default: \

98 v = *(const uint32_t *)ptr; \

99 break; \

100 } \

101 }

102

103

104 static int alloc_table(VLC *vlc, int size, int use_static)

105 {

106 int index = vlc->table_size;

107

108 vlc->table_size += size;

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

110 if (use_static)

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

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

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

114 if (!vlc->table)

115 return AVERROR(ENOMEM);

116 }

117 return index;

118 }

119

120 static av_always_inline uint32_t bitswap_32(uint32_t x)

121 {

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

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

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

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

126 }

127

128 typedef struct {

129 uint8_t bits;

130 uint16_t symbol;

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

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

133 uint32_t code;

134 } VLCcode;

135

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

137 {

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

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

140 }

141 /**

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

143 *

144 * @param vlc the context to be initted

145 *

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

147 * (Longer codes are delegated to subtables.)

148 *

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

150 *

151 * @param codes descriptions of the vlc codes

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

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

154 */

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

156 VLCcode *codes, int flags)

157 {

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

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

160 uint32_t code;

161 VLC_TYPE (*table)[2];

162

163 table_size = 1 << table_nb_bits;

164 if (table_nb_bits > 30)

165 return -1;

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

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

168 if (table_index < 0)

169 return table_index;

170 table = &vlc->table[table_index];

171

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

173 table[i][1] = 0; //bits

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

175 }

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

194 if (table[j][1] /*bits*/ != 0) {

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

196 return AVERROR_INVALIDDATA;

197 }

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

199 table[j][0] = symbol;

200 j += inc;

201 }

202 } else {

203 /* fill auxiliary table recursively */

204 n -= table_nb_bits;

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

206 subtable_bits = n;

207 codes[i].bits = n;

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

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

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

211 if (n <= 0)

212 break;

213 code = codes[k].code;

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

215 break;

216 codes[k].bits = n;

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

218 subtable_bits = FFMAX(subtable_bits, n);

219 }

220 subtable_bits = FFMIN(subtable_bits, table_nb_bits);

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

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

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

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

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

226 if (index < 0)

227 return index;

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

229 table = &vlc->table[table_index];

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

231 i = k-1;

232 }

233 }

234 return table_index;

235 }

236

237

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

239

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

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

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

243

244 'nb_codes' : number of vlcs codes

245

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

247

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

249

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

251

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

253 'bits' or 'codes' tables.

254

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

256 or 'codes' tables.

257

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

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

260

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

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

263 */

264 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,

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

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

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

268 int flags)

269 {

270 VLCcode *buf;

271 int i, j, ret;

272

273 vlc->bits = nb_bits;

274 if (flags & INIT_VLC_USE_NEW_STATIC) {

275 VLC dyn_vlc = *vlc;

276

277 if (vlc->table_size)

278 return 0;

279

280 ret = ff_init_vlc_sparse(&dyn_vlc, nb_bits, nb_codes,

281 bits, bits_wrap, bits_size,

282 codes, codes_wrap, codes_size,

283 symbols, symbols_wrap, symbols_size,

284 flags & ~INIT_VLC_USE_NEW_STATIC);

285 av_assert0(ret >= 0);

286 av_assert0(dyn_vlc.table_size <= vlc->table_allocated);

287 if (dyn_vlc.table_size < vlc->table_allocated)

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

289 memcpy(vlc->table, dyn_vlc.table, dyn_vlc.table_size * sizeof(*vlc->table));

290 vlc->table_size = dyn_vlc.table_size;

291 ff_free_vlc(&dyn_vlc);

292 return 0;

293 } else {

294 vlc->table = NULL;

295 vlc->table_allocated = 0;

296 vlc->table_size = 0;

297 }

298

299 av_dlog(NULL, "build table nb_codes=%d\n", nb_codes);

300

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

302 if (!buf)

303 return AVERROR(ENOMEM);

304

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

306 j = 0;

307 #define COPY(condition)\

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

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

310 if (!(condition)) \

311 continue; \

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

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

314 av_free(buf); \

315 return -1; \

316 } \

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

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

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

320 av_free(buf); \

321 return -1; \

322 } \

323 if (flags & INIT_VLC_LE) \

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

325 else \

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

327 if (symbols) \

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

329 else \

330 buf[j].symbol = i; \

331 j++; \

332 }

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

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

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

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

337 nb_codes = j;

338

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

340

341 av_free(buf);

342 if (ret < 0) {

343 av_freep(&vlc->table);

344 return ret;

345 }

346 return 0;

347 }

348

349

350 void ff_free_vlc(VLC *vlc)

351 {

352 av_freep(&vlc->table);

353 }

Generated on Wed Jul 10 2013 23:47:56 for FFmpeg by doxygen 1.8.2