ttystate.c

完整的EVRC压缩解压缩算法源码,附带一个简单的例子程序。

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

/*********************************************************************
*   get_tty_state()
*
**********************************************************************/
#include <stdio.h>
#include "typedef.h"
#include "tty.h"
#include "basic_op.h"


#define ONSET_BITS          2

void get_tty_state(
    Word16   *ttyState,              /* (i/o): TTY State                   */
    Word16   first_tty_char_flag,    /* (i): first char detected flag      */
    Word16   tty_bit_hist[],         /* (i): TTY bit history buffer        */
    Word16   tty_bit_len_hist[]      /* (i): TTY bit length history buffer */
)
{
    Word16   j;
    Word16   index;
    Word16   temp;



                                                                
    if( sub(tty_bit_len_hist[TTY_BIT_HIST_LEN-1],MIN_BIT_LEN) > 0 )
    {
        index = TTY_BIT_HIST_LEN-1;                             
    }
    else
    {
        index = STOP_BIT_IDX;                                   
    }

                                                                
    if( sub(tty_bit_hist[index],LOGIC_1) == 0
        && sub(tty_bit_hist[index-1],LOGIC_0) == 0 )
    {
        *ttyState = TTY_ONSET;                              
    }

    temp = index;                                           
    for( j=temp ; j >= START_BIT_IDX  ; j-- )
    {
                                                            
        if( sub(tty_bit_hist[j],LOGIC_0) == 0 )
        {
            temp = j;
        }
        else
        {
                                                            
            if( sub(tty_bit_hist[j],LOGIC_1) != 0 )
            {
                break;
            }
        }
    }

    /* Zero the bad dit counter */

    if( sub(temp,MEM_BIT_IDX) == 0 || sub(tty_bit_hist[temp],LOGIC_0) != 0 )
    {
        tty_bit_len_hist[MEM_BIT_IDX] = 0;
    }

    if( sub(tty_bit_hist[temp],LOGIC_0) != 0 )
    {
        for( j=0 ; j < TTY_BIT_HIST_LEN ; j++ )
        {
            tty_bit_hist[j] = UNKNOWN;
        }
    }

                                                            
    if( sub(temp,sub(index,ONSET_BITS-1)) > 0 )
    {
        *ttyState = NON_TTY_MODE;                       


        return;
    }
    else
    {
                                                           
        if( sub(temp,START_BIT_IDX) <= 0  )
        {
            *ttyState = NON_TTY_MODE;                       


            return;
        }
                                                            
        if( sub(first_tty_char_flag,1) == 0 )
        {
            *ttyState = TTY_ONSET;                              
        }
    }

                                                            
    if( sub(tty_bit_hist[TTY_BIT_HIST_LEN-1],UNKNOWN) == 0 )
    {
        *ttyState = NON_TTY_MODE;                           


        return;
    }



    return;
}