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_crc.cpp 25 26 Functions: 27 getbits_crc 28 calculate_crc 29 30 Date: 09/21/2007 31 32------------------------------------------------------------------------------ 33 REVISION HISTORY 34 35 36 Description: 37 38------------------------------------------------------------------------------ 39 INPUT AND OUTPUT DEFINITIONS 40 41getbits_crc 42 43Input 44 tbits *inputStream, bit stream structure 45 int32 neededBits, number of bits to read from the bit stream 46 uint32 *crc, memory location holding calculated crc value 47 uint32 crc_enabled flag to enable/disable crc checking 48 49------------------------------------------------------------------------------ 50 INPUT AND OUTPUT DEFINITIONS 51 52calculate_crc 53 54Input 55 uint32 data, data vector 56 uint32 length, number of element upon the crc will be calculated 57 uint32 *crc, memory location holding calculated crc value 58 59------------------------------------------------------------------------------ 60 FUNCTION DESCRIPTION 61 62 63------------------------------------------------------------------------------ 64 REQUIREMENTS 65 66 67------------------------------------------------------------------------------ 68 REFERENCES 69 70 [1] ISO MPEG Audio Subgroup Software Simulation Group (1996) 71 ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension 72 73------------------------------------------------------------------------------ 74 PSEUDO-CODE 75 76 ------------------------------------------------------------------------------ 77*/ 78 79 80/*---------------------------------------------------------------------------- 81; INCLUDES 82----------------------------------------------------------------------------*/ 83 84#include "pvmp3_getbits.h" 85#include "pvmp3_crc.h" 86 87/*---------------------------------------------------------------------------- 88; MACROS 89; Define module specific macros here 90----------------------------------------------------------------------------*/ 91 92 93/*---------------------------------------------------------------------------- 94; DEFINES 95; Include all pre-processor statements here. Include conditional 96; compile variables also. 97----------------------------------------------------------------------------*/ 98 99/*---------------------------------------------------------------------------- 100; LOCAL FUNCTION DEFINITIONS 101; Function Prototype declaration 102----------------------------------------------------------------------------*/ 103 104/*---------------------------------------------------------------------------- 105; LOCAL STORE/BUFFER/POINTER DEFINITIONS 106; Variable declaration - defined here and used outside this module 107----------------------------------------------------------------------------*/ 108 109/*---------------------------------------------------------------------------- 110; EXTERNAL FUNCTION REFERENCES 111; Declare functions defined elsewhere and referenced in this module 112----------------------------------------------------------------------------*/ 113 114/*---------------------------------------------------------------------------- 115; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES 116; Declare variables used in this module but defined elsewhere 117----------------------------------------------------------------------------*/ 118 119/*---------------------------------------------------------------------------- 120; FUNCTION CODE 121----------------------------------------------------------------------------*/ 122 123uint32 getbits_crc(tmp3Bits *inputStream, /* bit stream structure */ 124 int32 neededBits, /* number of bits to read from the bit stream */ 125 uint32 *crc, 126 uint32 crc_enabled) 127{ 128 uint32 bits = getNbits(inputStream, neededBits); 129 130 if (crc_enabled) 131 { 132 calculate_crc(bits, neededBits, crc); 133 } 134 return(bits); 135} 136 137/*---------------------------------------------------------------------------- 138; FUNCTION CODE 139----------------------------------------------------------------------------*/ 140 141void calculate_crc(uint32 data, 142 uint32 length, 143 uint32 *crc) 144{ 145 uint32 carry; 146 uint32 masking = 1 << length; 147 148 while ((masking >>= 1)) 149 { 150 carry = *crc & 0x8000; 151 *crc <<= 1; 152 if (!carry ^ !(data & masking)) 153 { 154 *crc ^= CRC16_POLYNOMIAL; 155 } 156 } 157 *crc &= 0xffff; 158} 159 160 161 162