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/* ------------------------------------------------------------------
* 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;
}
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