text: /* ------------------------------------------------------------------
   * 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_seek_synch.cpp
  
     Functions:
          pvmp3_seek_synch
          pvmp3_header_sync
  
  
       Date: 9/21/2007
  
  ------------------------------------------------------------------------------
   REVISION HISTORY
  
  
   Description:
  
  ------------------------------------------------------------------------------
   INPUT AND OUTPUT DEFINITIONS
  
  pvmp3_frame_synch
  
  Input
      pExt = pointer to the external interface structure. See the file
             pvmp3decoder_api.h for a description of each field.
             Data type of pointer to a tPVMP3DecoderExternal
             structure.
  
      pMem = void pointer to hide the internal implementation of the library
             It is cast back to a tmp3dec_file structure. This structure
             contains information that needs to persist between calls to
             this function, or is too big to be placed on the stack, even
             though the data is only needed during execution of this function
             Data type void pointer, internally pointer to a tmp3dec_file
             structure.
  
  
  ------------------------------------------------------------------------------
   FUNCTION DESCRIPTION
  
      search mp3 sync word, when found, it verifies, based on header parameters,
      the locations of the very next sync word,
      - if fails, then indicates a false sync,
      - otherwise, it confirm synchronization of at least 2 consecutives frames
  
  ------------------------------------------------------------------------------
   REQUIREMENTS
  
  
  ------------------------------------------------------------------------------
   REFERENCES
  
  ------------------------------------------------------------------------------
   PSEUDO-CODE
  
  ------------------------------------------------------------------------------
  */
  
  
  /*----------------------------------------------------------------------------
  ; INCLUDES
  ----------------------------------------------------------------------------*/
  
  #include "pvmp3_seek_synch.h"
  #include "pvmp3_getbits.h"
  #include "s_tmp3dec_file.h"
  #include "pv_mp3dec_fxd_op.h"
  #include "pvmp3_tables.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
  ----------------------------------------------------------------------------*/
  
  
  
  ERROR_CODE pvmp3_frame_synch(tPVMP3DecoderExternal *pExt,
                               void                  *pMem) /* bit stream structure */
  {
      uint16 val;
      ERROR_CODE err;
  
      tmp3dec_file      *pVars;
  
      pVars = (tmp3dec_file *)pMem;
  
      pVars->inputStream.pBuffer = pExt->pInputBuffer;
      pVars->inputStream.usedBits = (pExt->inputBufferUsedLength << 3); // in bits
  
  
      pVars->inputStream.inputBufferCurrentLength = (pExt->inputBufferCurrentLength); // in bits
  
      err = pvmp3_header_sync(&pVars->inputStream);
  
      if (err == NO_DECODING_ERROR)
      {
          /* validate synchronization by checking two consecutive sync words */
  
          // to avoid multiple bitstream accesses
          uint32 temp = getNbits(&pVars->inputStream, 21);
          // put back whole header
          pVars->inputStream.usedBits -= 21 + SYNC_WORD_LNGTH;
  
          int32  version;
  
          switch (temp >> 19)  /* 2 */
          {
              case 0:
                  version = MPEG_2_5;
                  break;
              case 2:
                  version = MPEG_2;
                  break;
              case 3:
                  version = MPEG_1;
                  break;
              default:
                  version = INVALID_VERSION;
                  break;
          }
  
          int32 freq_index = (temp << 20) >> 30;
  
          if (version != INVALID_VERSION && (freq_index != 3))
          {
              int32 numBytes = fxp_mul32_Q28(mp3_bitrate[version][(temp<<16)>>28] << 20,
                                             inv_sfreq[freq_index]);
  
              numBytes >>= (20 - version);
  
              if (version != MPEG_1)
              {
                  numBytes >>= 1;
              }
              if ((temp << 22) >> 31)
              {
                  numBytes++;
              }
  
              if (numBytes > (int32)pVars->inputStream.inputBufferCurrentLength)
              {
                  /* frame should account for padding and 2 bytes to check sync */
                  pExt->CurrentFrameLength = numBytes + 3;
                  return (SYNCH_LOST_ERROR);
              }
              else if (numBytes == (int32)pVars->inputStream.inputBufferCurrentLength)
              {
                  /* No enough data to validate, but current frame appears to be correct ( EOF case) */
                  pExt->inputBufferUsedLength = pVars->inputStream.usedBits >> 3;
                  return (NO_DECODING_ERROR);
              }
              else
              {
  
                  int32 offset = pVars->inputStream.usedBits + ((numBytes) << 3);
  
                  offset >>= INBUF_ARRAY_INDEX_SHIFT;
                  uint8    *pElem  = pVars->inputStream.pBuffer + offset;
                  uint16 tmp1 = *(pElem++);
                  uint16 tmp2 = *(pElem);
  
                  val = (tmp1 << 3);
                  val |= (tmp2 >> 5);
              }
          }
          else
          {
              val = 0; // force mismatch
          }
  
          if (val == SYNC_WORD)
          {
              pExt->inputBufferUsedLength = pVars->inputStream.usedBits >> 3; ///  !!!!!
              err = NO_DECODING_ERROR;
          }
          else
          {
              pExt->inputBufferCurrentLength = 0;
              err = SYNCH_LOST_ERROR;
          }
      }
      else
      {
          pExt->inputBufferCurrentLength = 0;
      }
  
      return(err);
  
  }
  
  /*
  ------------------------------------------------------------------------------
   REVISION HISTORY
  
  
   Description:
  
  ------------------------------------------------------------------------------
   INPUT AND OUTPUT DEFINITIONS
  
  pvmp3_header_sync
  
  Input
      tmp3Bits *inputStream,     structure holding the input stream parameters
  
  ------------------------------------------------------------------------------
   FUNCTION DESCRIPTION
  
      search mp3 sync word
  
  ------------------------------------------------------------------------------
   REQUIREMENTS
  
  
  ------------------------------------------------------------------------------
   REFERENCES
  
  ------------------------------------------------------------------------------
   PSEUDO-CODE
  
  ------------------------------------------------------------------------------
  */
  
  /*----------------------------------------------------------------------------
  ; FUNCTION CODE
  ----------------------------------------------------------------------------*/
  
  
  ERROR_CODE pvmp3_header_sync(tmp3Bits  *inputStream)
  {
      uint16 val;
      uint32 availableBits = (inputStream->inputBufferCurrentLength << 3); // in bits
  
      // byte aligment
      inputStream->usedBits = (inputStream->usedBits + 7) & 8;
  
      val = (uint16)getUpTo17bits(inputStream, SYNC_WORD_LNGTH);
  
      while (((val&SYNC_WORD) != SYNC_WORD) && (inputStream->usedBits < availableBits))
      {
          val <<= 8;
          val |= getUpTo9bits(inputStream, 8);
      }
  
      if ((val&SYNC_WORD) == SYNC_WORD && (inputStream->usedBits < availableBits))
      {
          return(NO_DECODING_ERROR);
      }
      else
      {
          return(SYNCH_LOST_ERROR);
      }
  
  }
  
  