/Avc/avc_bitstream.cpp
C++ | 276 lines | 145 code | 39 blank | 92 comment | 15 complexity | 430cd17351d8cf78566def824824b68b MD5 | raw file
1/* ------------------------------------------------------------------ 2 * Copyright (C) 1998-2009 PacketVideo 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either 13 * express or implied. 14 * See the License for the specific language governing permissions 15 * and limitations under the License. 16 * ------------------------------------------------------------------- 17 */ 18#include "avcdec_bitstream.h" 19 20/* Swapping may not be needed anymore since we read one byte at a time and perform 21EBSP to RBSP conversion in bitstream. */ 22#ifdef LITTLE_ENDIAN 23#if (WORD_SIZE==32) /* this can be replaced with assembly instructions */ 24#define SWAP_BYTES(x) ((((x)&0xFF)<<24) | (((x)&0xFF00)<<8) | (((x)&0xFF0000)>>8) | (((x)&0xFF000000)>>24)) 25#else /* for 16-bit */ 26#define SWAP_BYTES(x) ((((x)&0xFF)<<8) | (((x)&0xFF00)>>8)) 27#endif 28#else 29#define SWAP_BYTES(x) (x) 30#endif 31 32 33/* array for trailing bit pattern as function of number of bits */ 34/* the first one is unused. */ 35const static uint8 trailing_bits[9] = {0, 0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80}; 36 37/* ======================================================================== */ 38/* Function : BitstreamInit() */ 39/* Date : 11/4/2003 */ 40/* Purpose : Populate bitstream structure with bitstream buffer and size */ 41/* it also initializes internal data */ 42/* In/out : */ 43/* Return : AVCDEC_SUCCESS if successed, AVCDEC_FAIL if failed. */ 44/* Modified : */ 45/* ======================================================================== */ 46/* |--------|--------|----~~~~~-----|---------|---------|---------| 47 ^ ^read_pos ^data_end_pos 48 bitstreamBuffer <---------> 49 current_word 50 51 |xxxxxxxxxxxxx----| = current_word 32 or 16 bits 52 <------------> 53 bit_left 54 ======================================================================== */ 55 56 57/* ======================================================================== */ 58/* Function : BitstreamNextWord() */ 59/* Date : 12/4/2003 */ 60/* Purpose : Read up to machine word. */ 61/* In/out : */ 62/* Return : Next word with emulation prevention code removed. Everything 63 in the bitstream structure got modified except current_word */ 64/* Modified : */ 65/* ======================================================================== */ 66 67AVCDec_Status BitstreamInit(AVCDecBitstream *stream, uint8 *buffer, int size) 68{ 69 EBSPtoRBSP(buffer, &size); 70 71 stream->incnt = 0; 72 stream->incnt_next = 0; 73 stream->bitcnt = 0; 74 stream->curr_word = stream->next_word = 0; 75 stream->read_pos = 0; 76 77 stream->bitstreamBuffer = buffer; 78 79 stream->data_end_pos = size; 80 81 stream->nal_size = size; 82 83 return AVCDEC_SUCCESS; 84} 85/* ======================================================================== */ 86/* Function : AVC_BitstreamFillCache() */ 87/* Date : 1/1/2005 */ 88/* Purpose : Read up to machine word. */ 89/* In/out : */ 90/* Return : Read in 4 bytes of input data */ 91/* Modified : */ 92/* ======================================================================== */ 93 94AVCDec_Status AVC_BitstreamFillCache(AVCDecBitstream *stream) 95{ 96 uint8 *bitstreamBuffer = stream->bitstreamBuffer; 97 uint8 *v; 98 int num_bits, i; 99 100 stream->curr_word |= (stream->next_word >> stream->incnt); // stream->incnt cannot be 32 101 stream->next_word <<= (31 - stream->incnt); 102 stream->next_word <<= 1; 103 num_bits = stream->incnt_next + stream->incnt; 104 if (num_bits >= 32) 105 { 106 stream->incnt_next -= (32 - stream->incnt); 107 stream->incnt = 32; 108 return AVCDEC_SUCCESS; 109 } 110 /* this check can be removed if there is additional extra 4 bytes at the end of the bitstream */ 111 v = bitstreamBuffer + stream->read_pos; 112 113 if (stream->read_pos > stream->data_end_pos - 4) 114 { 115 if (stream->data_end_pos <= stream->read_pos) 116 { 117 stream->incnt = num_bits; 118 stream->incnt_next = 0; 119 return AVCDEC_SUCCESS; 120 } 121 122 stream->next_word = 0; 123 124 for (i = 0; i < stream->data_end_pos - stream->read_pos; i++) 125 { 126 stream->next_word |= (v[i] << ((3 - i) << 3)); 127 } 128 129 stream->read_pos = stream->data_end_pos; 130 stream->curr_word |= (stream->next_word >> num_bits); // this is safe 131 132 stream->next_word <<= (31 - num_bits); 133 stream->next_word <<= 1; 134 num_bits = i << 3; 135 stream->incnt += stream->incnt_next; 136 stream->incnt_next = num_bits - (32 - stream->incnt); 137 if (stream->incnt_next < 0) 138 { 139 stream->incnt += num_bits; 140 stream->incnt_next = 0; 141 } 142 else 143 { 144 stream->incnt = 32; 145 } 146 return AVCDEC_SUCCESS; 147 } 148 149 stream->next_word = ((uint32)v[0] << 24) | (v[1] << 16) | (v[2] << 8) | v[3]; 150 stream->read_pos += 4; 151 152 stream->curr_word |= (stream->next_word >> num_bits); // this is safe 153 stream->next_word <<= (31 - num_bits); 154 stream->next_word <<= 1; 155 stream->incnt_next += stream->incnt; 156 stream->incnt = 32; 157 return AVCDEC_SUCCESS; 158 159} 160/* ======================================================================== */ 161/* Function : BitstreamReadBits() */ 162/* Date : 11/4/2003 */ 163/* Purpose : Read up to machine word. */ 164/* In/out : */ 165/* Return : AVCDEC_SUCCESS if successed, AVCDEC_FAIL if number of bits */ 166/* is greater than the word-size, AVCDEC_PACKET_LOSS or */ 167/* AVCDEC_NO_DATA if callback to get data fails. */ 168/* Modified : */ 169/* ======================================================================== */ 170AVCDec_Status BitstreamReadBits(AVCDecBitstream *stream, int nBits, uint *code) 171{ 172 if (stream->incnt < nBits) 173 { 174 /* frame-based decoding */ 175 AVC_BitstreamFillCache(stream); 176 } 177 *code = stream->curr_word >> (32 - nBits); 178 BitstreamFlushBits(stream, nBits); 179 return AVCDEC_SUCCESS; 180} 181 182 183 184/* ======================================================================== */ 185/* Function : BitstreamShowBits() */ 186/* Date : 11/4/2003 */ 187/* Purpose : Show up to machine word without advancing the pointer. */ 188/* In/out : */ 189/* Return : AVCDEC_SUCCESS if successed, AVCDEC_FAIL if number of bits */ 190/* is greater than the word-size, AVCDEC_NO_DATA if it needs */ 191/* to callback to get data. */ 192/* Modified : */ 193/* ======================================================================== */ 194AVCDec_Status BitstreamShowBits(AVCDecBitstream *stream, int nBits, uint *code) 195{ 196 if (stream->incnt < nBits) 197 { 198 /* frame-based decoding */ 199 AVC_BitstreamFillCache(stream); 200 } 201 202 *code = stream->curr_word >> (32 - nBits); 203 204 return AVCDEC_SUCCESS; 205} 206 207/* ======================================================================== */ 208/* Function : BitstreamRead1Bit() */ 209/* Date : 11/4/2003 */ 210/* Purpose : Read 1 bit from the bitstream. */ 211/* In/out : */ 212/* Return : AVCDEC_SUCCESS if successed, AVCDEC_FAIL if number of bits */ 213/* is greater than the word-size, AVCDEC_PACKET_LOSS or */ 214/* AVCDEC_NO_DATA if callback to get data fails. */ 215/* Modified : */ 216/* ======================================================================== */ 217 218AVCDec_Status BitstreamRead1Bit(AVCDecBitstream *stream, uint *code) 219{ 220 if (stream->incnt < 1) 221 { 222 /* frame-based decoding */ 223 AVC_BitstreamFillCache(stream); 224 } 225 *code = stream->curr_word >> 31; 226 BitstreamFlushBits(stream, 1); 227 return AVCDEC_SUCCESS; 228} 229 230 231 232AVCDec_Status BitstreamByteAlign(AVCDecBitstream *stream) 233{ 234 uint n_stuffed; 235 236 n_stuffed = (8 - (stream->bitcnt & 0x7)) & 0x7; /* 07/05/01 */ 237 238 stream->bitcnt += n_stuffed; 239 stream->incnt -= n_stuffed; 240 241 if (stream->incnt < 0) 242 { 243 stream->bitcnt += stream->incnt; 244 stream->incnt = 0; 245 } 246 stream->curr_word <<= n_stuffed; 247 return AVCDEC_SUCCESS; 248} 249 250/* check whether there are more RBSP data. */ 251/* ignore the emulation prevention code, assume it has been taken out. */ 252bool more_rbsp_data(AVCDecBitstream *stream) 253{ 254 int total_bit_left; 255 uint code; 256 257 if (stream->read_pos >= stream->nal_size) 258 { 259 total_bit_left = stream->incnt_next + stream->incnt; 260 if (total_bit_left <= 0) 261 { 262 return FALSE; 263 } 264 else if (total_bit_left <= 8) 265 { 266 BitstreamShowBits(stream, total_bit_left, &code); 267 if (code == trailing_bits[total_bit_left]) 268 { 269 return FALSE; 270 } 271 } 272 } 273 274 return TRUE; 275} 276