| /* ------------------------------------------------------------------ |
| * Copyright (C) 1998-2009 PacketVideo |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either |
| * express or implied. |
| * See the License for the specific language governing permissions |
| * and limitations under the License. |
| * ------------------------------------------------------------------- |
| */ |
| /* |
| ------------------------------------------------------------------------------ |
| |
| PacketVideo Corp. |
| MP3 Decoder Library |
| |
| Filename: pvmp3_crc.cpp |
| |
| Functions: |
| getbits_crc |
| calculate_crc |
| |
| Date: 09/21/2007 |
| |
| ------------------------------------------------------------------------------ |
| REVISION HISTORY |
| |
| |
| Description: |
| |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| getbits_crc |
| |
| Input |
| tbits *inputStream, bit stream structure |
| int32 neededBits, number of bits to read from the bit stream |
| uint32 *crc, memory location holding calculated crc value |
| uint32 crc_enabled flag to enable/disable crc checking |
| |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| calculate_crc |
| |
| Input |
| uint32 data, data vector |
| uint32 length, number of element upon the crc will be calculated |
| uint32 *crc, memory location holding calculated crc value |
| |
| ------------------------------------------------------------------------------ |
| FUNCTION DESCRIPTION |
| |
| |
| ------------------------------------------------------------------------------ |
| REQUIREMENTS |
| |
| |
| ------------------------------------------------------------------------------ |
| REFERENCES |
| |
| [1] ISO MPEG Audio Subgroup Software Simulation Group (1996) |
| ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension |
| |
| ------------------------------------------------------------------------------ |
| PSEUDO-CODE |
| |
| ------------------------------------------------------------------------------ |
| */ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; INCLUDES |
| ----------------------------------------------------------------------------*/ |
| |
| #include "pvmp3_getbits.h" |
| #include "pvmp3_crc.h" |
| |
| /*---------------------------------------------------------------------------- |
| ; MACROS |
| ; Define module specific macros here |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; DEFINES |
| ; Include all pre-processor statements here. Include conditional |
| ; compile variables also. |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; LOCAL FUNCTION DEFINITIONS |
| ; Function Prototype declaration |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; LOCAL STORE/BUFFER/POINTER DEFINITIONS |
| ; Variable declaration - defined here and used outside this module |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; EXTERNAL FUNCTION REFERENCES |
| ; Declare functions defined elsewhere and referenced in this module |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES |
| ; Declare variables used in this module but defined elsewhere |
| ----------------------------------------------------------------------------*/ |
| |
| /*---------------------------------------------------------------------------- |
| ; FUNCTION CODE |
| ----------------------------------------------------------------------------*/ |
| |
| uint32 getbits_crc(tmp3Bits *inputStream, /* bit stream structure */ |
| int32 neededBits, /* number of bits to read from the bit stream */ |
| uint32 *crc, |
| uint32 crc_enabled) |
| { |
| uint32 bits = getNbits(inputStream, neededBits); |
| |
| if (crc_enabled) |
| { |
| calculate_crc(bits, neededBits, crc); |
| } |
| return(bits); |
| } |
| |
| /*---------------------------------------------------------------------------- |
| ; FUNCTION CODE |
| ----------------------------------------------------------------------------*/ |
| |
| void calculate_crc(uint32 data, |
| uint32 length, |
| uint32 *crc) |
| { |
| uint32 carry; |
| uint32 masking = 1 << length; |
| |
| while ((masking >>= 1)) |
| { |
| carry = *crc & 0x8000; |
| *crc <<= 1; |
| if (!carry ^ !(data & masking)) |
| { |
| *crc ^= CRC16_POLYNOMIAL; |
| } |
| } |
| *crc &= 0xffff; |
| } |
| |
| |
| |