libSBRdec/src/sbr_crc.cpp

/* -----------------------------------------------------------------------------------------------------------
Software License for The Fraunhofer FDK AAC Codec Library for Android

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----------------------------------------------------------------------------------------------------------- */

/*!
  \file
  \brief  CRC check coutines  
*/

#include "sbr_crc.h"

#include "FDK_bitstream.h"
#include "transcendent.h"

#define MAXCRCSTEP    16
#define MAXCRCSTEP_LD  4

/*!
  \brief     crc calculation
*/
static ULONG
calcCRC (HANDLE_CRC hCrcBuf, ULONG bValue, int nBits)
{
  int i;
  ULONG bMask = (1UL << (nBits - 1));

  for (i = 0; i < nBits; i++, bMask >>= 1) {
    USHORT flag = (hCrcBuf->crcState & hCrcBuf->crcMask) ? 1 : 0;
    USHORT flag1 = (bMask & bValue) ? 1 : 0;

    flag ^= flag1;
    hCrcBuf->crcState <<= 1;
    if (flag)
      hCrcBuf->crcState ^= hCrcBuf->crcPoly;
  }

  return (hCrcBuf->crcState);
}


/*!
  \brief     crc
*/
static int
getCrc (HANDLE_FDK_BITSTREAM hBs, ULONG NrBits)
{
  int i;
  CRC_BUFFER CrcBuf;

  CrcBuf.crcState = SBR_CRC_START;
  CrcBuf.crcPoly  = SBR_CRC_POLY;
  CrcBuf.crcMask  = SBR_CRC_MASK;

  int CrcStep = NrBits>>MAXCRCSTEP_LD;

  int CrcNrBitsRest = (NrBits - CrcStep * MAXCRCSTEP);
  ULONG bValue;

  for (i = 0; i < CrcStep; i++) {
    bValue = FDKreadBits (hBs, MAXCRCSTEP);
    calcCRC (&CrcBuf, bValue, MAXCRCSTEP);
  }

  bValue = FDKreadBits (hBs, CrcNrBitsRest);
  calcCRC (&CrcBuf, bValue, CrcNrBitsRest);

  return (CrcBuf.crcState & SBR_CRC_RANGE);

}


/*!
  \brief   crc interface
  \return  1: CRC OK, 0: CRC check failure
*/
int
SbrCrcCheck (HANDLE_FDK_BITSTREAM hBs, /*!< handle to bit-buffer  */
             LONG NrBits)              /*!< max. CRC length       */
{
  int crcResult = 1;
  ULONG NrCrcBits;
  ULONG crcCheckResult;
  LONG NrBitsAvailable;
  ULONG crcCheckSum;

  crcCheckSum = FDKreadBits (hBs, 10);

  NrBitsAvailable = FDKgetValidBits(hBs);
  if (NrBitsAvailable <= 0){
    return 0;
  }

  NrCrcBits = fixMin ((INT)NrBits, (INT)NrBitsAvailable);

  crcCheckResult = getCrc (hBs, NrCrcBits);
  FDKpushBack(hBs, (NrBitsAvailable - FDKgetValidBits(hBs)) );


  if (crcCheckResult != crcCheckSum) {
    crcResult = 0;
  }

  return (crcResult);
}