libSBRdec/src/sbr_crc.cpp

   1
   2 /* -----------------------------------------------------------------------------------------------------------
   3 Software License for The Fraunhofer FDK AAC Codec Library for Android
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   5 © Copyright  1995 - 2013 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
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   9 The Fraunhofer FDK AAC Codec Library for Android ("FDK AAC Codec") is software that implements
  10 the MPEG Advanced Audio Coding ("AAC") encoding and decoding scheme for digital audio.
  11 This FDK AAC Codec software is intended to be used on a wide variety of Android devices.
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  75 Fraunhofer Institute for Integrated Circuits IIS
  76 Attention: Audio and Multimedia Departments - FDK AAC LL
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  82 ----------------------------------------------------------------------------------------------------------- */
  83
  84 /*!
  85   \file
  86   \brief  CRC check coutines
  87 */
  88
  89 #include "sbr_crc.h"
  90
  91 #include "FDK_bitstream.h"
  92 #include "transcendent.h"
  93
  94 #define MAXCRCSTEP    16
  95 #define MAXCRCSTEP_LD  4
  96
  97 /*!
  98   \brief     crc calculation
  99 */
 100 static ULONG
 101 calcCRC (HANDLE_CRC hCrcBuf, ULONG bValue, int nBits)
 102 {
 103   int i;
 104   ULONG bMask = (1UL << (nBits - 1));
 105
 106   for (i = 0; i < nBits; i++, bMask >>= 1) {
 107     USHORT flag = (hCrcBuf->crcState & hCrcBuf->crcMask) ? 1 : 0;
 108     USHORT flag1 = (bMask & bValue) ? 1 : 0;
 109
 110     flag ^= flag1;
 111     hCrcBuf->crcState <<= 1;
 112     if (flag)
 113       hCrcBuf->crcState ^= hCrcBuf->crcPoly;
 114   }
 115
 116   return (hCrcBuf->crcState);
 117 }
 118
 119
 120 /*!
 121   \brief     crc
 122 */
 123 static int
 124 getCrc (HANDLE_FDK_BITSTREAM hBs, ULONG NrBits)
 125 {
 126   int i;
 127   CRC_BUFFER CrcBuf;
 128
 129   CrcBuf.crcState = SBR_CRC_START;
 130   CrcBuf.crcPoly  = SBR_CRC_POLY;
 131   CrcBuf.crcMask  = SBR_CRC_MASK;
 132
 133   int CrcStep = NrBits>>MAXCRCSTEP_LD;
 134
 135   int CrcNrBitsRest = (NrBits - CrcStep * MAXCRCSTEP);
 136   ULONG bValue;
 137
 138   for (i = 0; i < CrcStep; i++) {
 139     bValue = FDKreadBits (hBs, MAXCRCSTEP);
 140     calcCRC (&CrcBuf, bValue, MAXCRCSTEP);
 141   }
 142
 143   bValue = FDKreadBits (hBs, CrcNrBitsRest);
 144   calcCRC (&CrcBuf, bValue, CrcNrBitsRest);
 145
 146   return (CrcBuf.crcState & SBR_CRC_RANGE);
 147
 148 }
 149
 150
 151 /*!
 152   \brief   crc interface
 153   \return  1: CRC OK, 0: CRC check failure
 154 */
 155 int
 156 SbrCrcCheck (HANDLE_FDK_BITSTREAM hBs, /*!< handle to bit-buffer  */
 157              LONG NrBits)              /*!< max. CRC length       */
 158 {
 159   int crcResult = 1;
 160   ULONG NrCrcBits;
 161   ULONG crcCheckResult;
 162   LONG NrBitsAvailable;
 163   ULONG crcCheckSum;
 164
 165   crcCheckSum = FDKreadBits (hBs, 10);
 166
 167   NrBitsAvailable = FDKgetValidBits(hBs);
 168   if (NrBitsAvailable <= 0){
 169     return 0;
 170   }
 171
 172   NrCrcBits = fixMin ((INT)NrBits, (INT)NrBitsAvailable);
 173
 174   crcCheckResult = getCrc (hBs, NrCrcBits);
 175   FDKpushBack(hBs, (NrBitsAvailable - FDKgetValidBits(hBs)) );
 176
 177
 178   if (crcCheckResult != crcCheckSum) {
 179     crcResult = 0;
 180   }
 181
 182   return (crcResult);
 183 }