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 /* 19 ------------------------------------------------------------------------------ 20 21 PacketVideo Corp. 22 MP3 Decoder Library 23 24 Filename: pvmp3_getbits.cpp 25 26 27 Date: 09/21/2007 28 29 ------------------------------------------------------------------------------ 30 REVISION HISTORY 31 32 33 Description: 34 35 ------------------------------------------------------------------------------ 36 INPUT AND OUTPUT DEFINITIONS 37 38 Inputs: 39 40 tmp3Bits *inputStream, structure holding the input stream parameters 41 int32 neededBits number of bits to read from the bit stream 42 43 Outputs: 44 45 word parsed from teh bitstream, with size neededBits-bits, 46 47 ------------------------------------------------------------------------------ 48 FUNCTION DESCRIPTION 49 50 51 ------------------------------------------------------------------------------ 52 REQUIREMENTS 53 54 55 ------------------------------------------------------------------------------ 56 REFERENCES 57 [1] ISO MPEG Audio Subgroup Software Simulation Group (1996) 58 ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension 59 60 61 ------------------------------------------------------------------------------ 62 PSEUDO-CODE 63 64 ------------------------------------------------------------------------------ 65 */ 66 67 /*---------------------------------------------------------------------------- 68 ; INCLUDES 69 ----------------------------------------------------------------------------*/ 70 #include "pvmp3_getbits.h" 71 72 /*---------------------------------------------------------------------------- 73 ; MACROS 74 ; Define module specific macros here 75 ----------------------------------------------------------------------------*/ 76 77 78 /*---------------------------------------------------------------------------- 79 ; DEFINES 80 ; Include all pre-processor statements here. Include conditional 81 ; compile variables also. 82 ----------------------------------------------------------------------------*/ 83 84 85 /*---------------------------------------------------------------------------- 86 ; LOCAL FUNCTION DEFINITIONS 87 ; Function Prototype declaration 88 ----------------------------------------------------------------------------*/ 89 90 /*---------------------------------------------------------------------------- 91 ; LOCAL STORE/BUFFER/POINTER DEFINITIONS 92 ; Variable declaration - defined here and used outside this module 93 ----------------------------------------------------------------------------*/ 94 95 /*---------------------------------------------------------------------------- 96 ; EXTERNAL FUNCTION REFERENCES 97 ; Declare functions defined elsewhere and referenced in this module 98 ----------------------------------------------------------------------------*/ 99 100 /*---------------------------------------------------------------------------- 101 ; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES 102 ; Declare variables used in this module but defined elsewhere 103 ----------------------------------------------------------------------------*/ 104 105 106 /*---------------------------------------------------------------------------- 107 ; FUNCTION CODE 108 ----------------------------------------------------------------------------*/ 109 110 uint32 getNbits(tmp3Bits *ptBitStream, 111 int32 neededBits) /* number of bits to read from the bitstream (up to 25) */ 112 { 113 114 uint32 offset; 115 uint32 bitIndex; 116 uint8 Elem; /* Needs to be same type as pInput->pBuffer */ 117 uint8 Elem1; 118 uint8 Elem2; 119 uint8 Elem3; 120 uint32 returnValue = 0; 121 122 if (!neededBits) 123 { 124 return (returnValue); 125 } 126 127 offset = (ptBitStream->usedBits) >> INBUF_ARRAY_INDEX_SHIFT; 128 129 Elem = *(ptBitStream->pBuffer + module(offset , BUFSIZE)); 130 Elem1 = *(ptBitStream->pBuffer + module(offset + 1, BUFSIZE)); 131 Elem2 = *(ptBitStream->pBuffer + module(offset + 2, BUFSIZE)); 132 Elem3 = *(ptBitStream->pBuffer + module(offset + 3, BUFSIZE)); 133 134 135 returnValue = (((uint32)(Elem)) << 24) | 136 (((uint32)(Elem1)) << 16) | 137 (((uint32)(Elem2)) << 8) | 138 ((uint32)(Elem3)); 139 140 /* Remove extra high bits by shifting up */ 141 bitIndex = module(ptBitStream->usedBits, INBUF_BIT_WIDTH); 142 143 /* This line is faster than to mask off the high bits. */ 144 returnValue <<= bitIndex; 145 146 /* Move the field down. */ 147 returnValue >>= (32 - neededBits); 148 149 ptBitStream->usedBits += neededBits; 150 151 return (returnValue); 152 } 153 154 /*---------------------------------------------------------------------------- 155 ; FUNCTION CODE 156 ----------------------------------------------------------------------------*/ 157 158 uint16 getUpTo9bits(tmp3Bits *ptBitStream, 159 int32 neededBits) /* number of bits to read from the bit stream 2 to 9 */ 160 { 161 162 uint32 offset; 163 uint32 bitIndex; 164 uint8 Elem; /* Needs to be same type as pInput->pBuffer */ 165 uint8 Elem1; 166 uint16 returnValue; 167 168 offset = (ptBitStream->usedBits) >> INBUF_ARRAY_INDEX_SHIFT; 169 170 Elem = *(ptBitStream->pBuffer + module(offset , BUFSIZE)); 171 Elem1 = *(ptBitStream->pBuffer + module(offset + 1, BUFSIZE)); 172 173 174 returnValue = (((uint16)(Elem)) << 8) | 175 ((uint16)(Elem1)); 176 177 /* Remove extra high bits by shifting up */ 178 bitIndex = module(ptBitStream->usedBits, INBUF_BIT_WIDTH); 179 180 ptBitStream->usedBits += neededBits; 181 /* This line is faster than to mask off the high bits. */ 182 returnValue = (returnValue << (bitIndex)); 183 184 /* Move the field down. */ 185 186 return (uint16)(returnValue >> (16 - neededBits)); 187 188 } 189 190 /*---------------------------------------------------------------------------- 191 ; FUNCTION CODE 192 ----------------------------------------------------------------------------*/ 193 194 uint32 getUpTo17bits(tmp3Bits *ptBitStream, 195 int32 neededBits) /* number of bits to read from the bit stream 2 to 8 */ 196 { 197 198 uint32 offset; 199 uint32 bitIndex; 200 uint8 Elem; /* Needs to be same type as pInput->pBuffer */ 201 uint8 Elem1; 202 uint8 Elem2; 203 uint32 returnValue; 204 205 offset = (ptBitStream->usedBits) >> INBUF_ARRAY_INDEX_SHIFT; 206 207 Elem = *(ptBitStream->pBuffer + module(offset , BUFSIZE)); 208 Elem1 = *(ptBitStream->pBuffer + module(offset + 1, BUFSIZE)); 209 Elem2 = *(ptBitStream->pBuffer + module(offset + 2, BUFSIZE)); 210 211 212 returnValue = (((uint32)(Elem)) << 16) | 213 (((uint32)(Elem1)) << 8) | 214 ((uint32)(Elem2)); 215 216 /* Remove extra high bits by shifting up */ 217 bitIndex = module(ptBitStream->usedBits, INBUF_BIT_WIDTH); 218 219 ptBitStream->usedBits += neededBits; 220 /* This line is faster than to mask off the high bits. */ 221 returnValue = 0xFFFFFF & (returnValue << (bitIndex)); 222 223 /* Move the field down. */ 224 225 return (uint32)(returnValue >> (24 - neededBits)); 226 227 } 228 229 /*---------------------------------------------------------------------------- 230 ; FUNCTION CODE 231 ----------------------------------------------------------------------------*/ 232 233 uint8 get1bit(tmp3Bits *ptBitStream) /* number of bits to read from the bit stream */ 234 { 235 236 uint32 offset; 237 uint32 bitIndex; 238 uint8 returnValue; 239 240 offset = (ptBitStream->usedBits) >> INBUF_ARRAY_INDEX_SHIFT; 241 242 returnValue = *(ptBitStream->pBuffer + module(offset , BUFSIZE)); 243 244 /* Remove extra high bits by shifting up */ 245 bitIndex = module(ptBitStream->usedBits, INBUF_BIT_WIDTH); 246 ptBitStream->usedBits++; 247 248 /* This line is faster than to mask off the high bits. */ 249 returnValue = (returnValue << (bitIndex)); 250 251 return (uint8)(returnValue >> 7); 252 253 } 254 255 256 257 258
