tty_dec.c

完整的EVRC压缩解压缩算法源码,通过C-C++编译后可以运行!

                                                         
                if( sub(num,best_num) > 0 )
                {
                    best_num = num;                      
                    best_counter = counter_hist[i];      
                    best_char = char_hist[i];            
                    best_rate = tty_rate_hist[i];      
                }
            }
        }
                                                            
        /* If best guess is silence */
        if( ((best_counter & (TTY_SILENCE|NON_TTY|TTY_EIGHTH_RATE|TTY_ONSET)) != 0)
            || ( sub(best_counter,counter_hist[CURRENT_FRAME+1]) == 0
                 && sub(best_char,char_hist[CURRENT_FRAME+1]) == 0 )
          )
        {
            /* Fix only this FER */
            counter_hist[CURRENT_FRAME] = best_counter; 
            char_hist[CURRENT_FRAME] = best_char;       
            tty_rate_hist[CURRENT_FRAME] = best_rate;               
        }
        else
        {
            /*** BEGIN: Not included in SMV TTY code ***/
            if( counter_hist[CURRENT_FRAME+1] == NON_TTY )
            {

                DEBUG(1,fprintf(stdout,"tty_dec(): Force NON_TTY, silence missing.\n");)
                counter_hist[CURRENT_FRAME] = NON_TTY;
                char_hist[CURRENT_FRAME] = 0;
            }
            else
            {
            /*** END: Not included in SMV TTY code ***/

                /* else fix a character's worth of frames */
 
                if( best_rate == 0 )
                {
                    /* Correct min of 7 frames for 45.45 baud */
                    error = sub(CURRENT_FRAME,7);           
                }
                else
                {
                    /* Correct min of 6 frames 50 baud */
                    error = sub(CURRENT_FRAME,6);
                }

                for( i=CURRENT_FRAME ; i >= 0 ; i-- )
                {
                                                            
                    if( sub(i,error) > 0
                        || sub(counter_hist[i],best_counter) == 0
                        || (counter_hist[i] & (TTY_FER|NON_TTY)) != 0 )
                    {
                        counter_hist[i] = best_counter;         
                        char_hist[i] = best_char;               
                        tty_rate_hist[i] = best_rate;           
                    }
                    else if( sub(counter_hist[i],best_counter) != 0
                         && (counter_hist[i] & COUNTER_BETWEEN_START_STOP) != 0 )
                    {
                        break;
                    }
                }
            }
        }
    }

                                                            
    /* if eighth rate, keep doing what was done in the last frame */
    if( sub(counter_hist[CURRENT_FRAME],TTY_EIGHTH_RATE) == 0 )
    {
        counter_hist[CURRENT_FRAME] = counter_hist[CURRENT_FRAME+1];    
        char_hist[CURRENT_FRAME] = char_hist[CURRENT_FRAME+1];          
        tty_rate_hist[CURRENT_FRAME] = tty_rate_hist[CURRENT_FRAME+1];          
    }

    /*****************************************************************
    * If NON_TTY is coming and there is trailing silence, get rid
    * of the silence.  This helps return to NON_TTY if there was
    * a false alarm
    ******************************************************************/

                                                            
    if( sub(counter_hist[0],NON_TTY) == 0 )
    {
        for( i=1 ; i <= CURRENT_FRAME ; i++ )
        {
                                                            
            if( counter_hist[i] == TTY_SILENCE )
            {
                counter_hist[i] = NON_TTY;                  
            }
            else
            {
                break;
            }
        }
    }

    /*** BEGIN: Not included in SMV TTY code ***/

    /*****************************************************************
    * Anticipate the transition from NON_TTY to TTY_SILENCE by
    * looking ahead when the mode is NON_TTY and vote on the presence
    * of TTY_SILENCE.  If there is a majority of TTY_SILENCE, change
    * the rest of the history buffer from NON_TTY to TTY_SILENCE.
    ******************************************************************/

    /*
    *  Added if() statement to improve performance in poor C/I conditions
    *  Do not convert to silence if the output is already silence.
    */
    if( counter_hist[CURRENT_FRAME] != TTY_SILENCE )
    {

        /* Count the number of silence frames */
        error = 0;                                              
        for( i=0 ; i <= CONVERT_TO_SILENCE_THRESH+1 ; i++ )
        {
            if( counter_hist[CONVERT_TO_SILENCE_THRESH+1-i] == TTY_SILENCE )
            {
                error++;
            }
            else if( counter_hist[CONVERT_TO_SILENCE_THRESH+1-i] == NON_TTY )
            {
                /* Start over if NON_TTY in middle of silence */
                error = 0;
            }
        }

        /* Convert NON_TTY, 8th rate, and FERs to silence */
        if( error >= CONVERT_TO_SILENCE_THRESH )
        {

            for( i=0 ; i <= CURRENT_FRAME ; i++ )
            {
                if( counter_hist[i] == NON_TTY
                    || counter_hist[i] == TTY_EIGHTH_RATE
                    || counter_hist[i] == TTY_FER
                  )
                {
                    counter_hist[i] = TTY_SILENCE;
                    char_hist[i] = TTY_SILENCE_CHAR;
                }
            }

        }
    }

    /*** END: Not included in SMV TTY code ***/

/*----------------------------------------------------------------*/
DEBUG(1,
    for( i=0 ; i < TTY_BUF_SIZE ; i++ )
    {
        if( counter_hist[i] == NON_TTY )
            fprintf(stdout,"( non )");
        else if( counter_hist[i] == TTY_FER )
            fprintf(stdout,"( FER )");
        else if( counter_hist[i] == TTY_SILENCE && char_hist[i] == TTY_SILENCE_CHAR)
            fprintf(stdout," slnce ");
        else if( counter_hist[i] == TTY_ONSET && char_hist[i] == TTY_ONSET_CHAR)
            fprintf(stdout," onset ");
        else if( counter_hist[i] == TTY_EIGHTH_RATE )
            fprintf(stdout,"( 8th )");
        else
            fprintf(stdout,"(%2d,%2d)",10*tty_rate_hist[i]+counter_hist[i],char_hist[i]);
    }
    fprintf(stdout,"__\n");

    if( counter_hist[CURRENT_FRAME] == TTY_FER )
    {
        fprintf(stdout,"Uncorrected FER.\n");
        counter_hist[CURRENT_FRAME] = TTY_SILENCE;
        char_hist[CURRENT_FRAME] = TTY_SILENCE_CHAR;
    }

)/* end DEBUG() */
/*----------------------------------------------------------------*/


  } /* end if(subframe == 0) */
  else
  {
                                                        
    /* If acb_gain is non-zero at any time in the frame, declare NON_TTY */
    if( acb_gain != 0 && !fer_flag )
    {
        counter_hist[0] = NON_TTY;                      
        char_hist[0] = 0;                               
    }
  }

  /* Generate the Baudot signal */
  i = tty_gen( buf,
               length,
               subframe,
               num_subfr,
               counter_hist,
               char_hist,
               tty_rate_hist );




  return(i);

} /* end tty_dec() */