tty_rate.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!

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/*************************************************************************
* tty_rate()
*   After a character is framed, tty_rate() decides if the character is
*   50 baud or 45.45 baud Baudot code.
**************************************************************************/

#include <stdio.h>
#include "typedef.h"
#include "tty.h"
#include "basic_op.h"


#define TTY_RATE_THRESH         63
#define TTY_RATE_THRESH_2       71
#define MAX_TTY_BAUD_COUNT      3


void tty_rate(
    Word16   *tty_baud_rate,     /* (i/o): prev/new tty baud rate    */
    Word16   tty_bit_len_hist[]  /* (i): bit len buffer              */
)
{
    Word16   i;
    Word16   char_len;

    static Word16    tty_baud_count = MAX_TTY_BAUD_COUNT;


    char_len = 0;                                           
    for( i=START_BIT_IDX ; i < STOP_BIT_IDX ; i++ )
    {
        char_len = add(char_len,tty_bit_len_hist[i]);
    }

    if( sub(char_len,TTY_RATE_THRESH) >= 0 )
    {
        i = TTY_45_BAUD;                                    

	/* 
	* Add the stop bit length and test the total
	* length.  If it is much too short for 45.45
	* baud, change it to 50 baud.
	*/
        char_len = add(char_len,tty_bit_len_hist[STOP_BIT_IDX]);
    if( sub(char_len,TTY_RATE_THRESH_2) < 0 )
	{
	    i = TTY_50_BAUD;
	}
    }
    else
    {
        i = TTY_50_BAUD;                                
    }
                                                        
    if( sub(i,*tty_baud_rate) == 0 )
    {
        tty_baud_count = MAX_TTY_BAUD_COUNT;            
    }
    else
    {
        /*
        *  Switch baud rates if the new rate occured
        *  3 characters in a row.
        */

        tty_baud_count = sub(tty_baud_count,1);
                                                            
        if( tty_baud_count <= 0 )
        {            
            *tty_baud_rate = i;                             
        }
    }


} /* end tty_rate() */