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_decode_header.cpp
  
       Date: 09/21/2007
  
  ------------------------------------------------------------------------------
   REVISION HISTORY
  
  
   Description:
  
  ------------------------------------------------------------------------------
   INPUT AND OUTPUT DEFINITIONS
  
  Input
      tbits  *inputStream,        bit stream
      mp3Header  *info,
      uint32 *crc
   Returns
  
      mp3Header  *info,           structure holding the parsed mp3 header info
      uint32 *crc                 initialized crc computation
  
  
  ------------------------------------------------------------------------------
   FUNCTION DESCRIPTION
  
      gets mp3 header information
  
  ------------------------------------------------------------------------------
   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_decode_header.h"
  #include "pvmp3_crc.h"
  #include "pvmp3_getbits.h"
  #include "pvmp3_seek_synch.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_decode_header(tmp3Bits  *inputStream,
                                 mp3Header  *info,
                                 uint32 *crc)
  {
  
      ERROR_CODE err = NO_DECODING_ERROR;
      uint32  temp;
  
      /*
       * Verify that at least the header is complete
       * Note that SYNC_WORD_LNGTH is in unit of bits, but inputBufferCurrentLength
       * is in unit of bytes.
       */
      if (inputStream->inputBufferCurrentLength < ((SYNC_WORD_LNGTH + 21) >> 3))
      {
          return NO_ENOUGH_MAIN_DATA_ERROR;
      }
  
      /*
       *  MPEG Audio Version ID
       */
      temp = getUpTo17bits(inputStream, SYNC_WORD_LNGTH);
      if ((temp & SYNC_WORD) != SYNC_WORD)
      {
          err = pvmp3_header_sync(inputStream);
  
          if (err != NO_DECODING_ERROR)
          {
              return err;
          }
      }
  
      temp = getNbits(inputStream, 21);   // to avoid multiple bitstream accesses
  
  
      switch (temp >> 19)  /* 2 */
      {
          case 0:
              info->version_x = MPEG_2_5;
              break;
          case 2:
              info->version_x = MPEG_2;
              break;
          case 3:
              info->version_x = MPEG_1;
              break;
          default:
              info->version_x = INVALID_VERSION;
              err = UNSUPPORTED_LAYER;
              break;
      }
  
      info->layer_description  = 4 - ((temp << 13) >> 30);  /* 2 */
      info->error_protection   =  !((temp << 15) >> 31);  /* 1 */
  
      if (info->error_protection)
      {
          *crc = 0xffff;           /* CRC start value */
          calculate_crc((temp << 16) >> 16, 16, crc);
      }
  
      info->bitrate_index      = (temp << 16) >> 28;  /* 4 */
      info->sampling_frequency = (temp << 20) >> 30;  /* 2 */
      info->padding            = (temp << 22) >> 31;  /* 1 */
      info->extension          = (temp << 23) >> 31;  /* 1 */
      info->mode               = (temp << 24) >> 30;  /* 2 */
      info->mode_ext           = (temp << 26) >> 30;  /* 2 */
      info->copyright          = (temp << 27) >> 31;  /* 1 */
      info->original           = (temp << 28) >> 31;  /* 1 */
      info->emphasis           = (temp << 30) >> 30;  /* 2 */
  
  
      if (!info->bitrate_index || info->sampling_frequency == 3)
      {
          err = UNSUPPORTED_FREE_BITRATE;
      }
  
      return(err);
  }
  
  