iir_fixpt_ccs.c

用dsp解压mp3程序的算法

/*****************************************************************
*  iir_fixpt_ccs.c- Fixed-point C program for IIR filtering using
*                   direct-form II biquads for CCS of C5000
*                   in Section 7.7.4
******************************************************************
*  System configuration:
* 
* in(n) |----------------| out(n)
*  ---->| Bandpass filter|----->
*       |----------------|
*
*     in(n) is the input data from data file "in_int_ccs.dat"
*
*****************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "iircoeff_ccs_16.h"  // coefficient header file  

int in_buffer[300];
int out_buffer[300];
#define TRUE 1

/*Function */
static int iirproc(int *input, int *output);
static void dataIO(void);

void main()
{
  /***************************************************************
  *    Declare file pointers
  ***************************************************************/

  int *input = &in_buffer[0];
  int *output= &out_buffer[0];
  
  /***************************************************************
  *    Start of main program
  ***************************************************************/
 
  while(TRUE)
  {           /* read in x(n) from data file and processing it  */
    dataIO();
    iirproc(input, output);  
  }
}


/*    Function for IIR filtering    */
static int iirproc(int *input, int *output)
{
  /***************************************************************
  *    Define variable arrays, define and clear variables
  ***************************************************************/
  const int section = 3;
  long out = 0;              /* y(n), output from IIR filter    */
  int delay[9] = {0,0,0,0,0,0,0,0,0};
  int gain = 17;
  int j;
  int size = 300;

  while(size--){          
    out=(long)((int)(((long)*input++ * (long)gain)>>15)); 

    /*************************************************************
    *    IIR filtering: feedback follow by feedforward and repeat
    *         for three sections.
    *************************************************************/
    
    for (j=0; j<section; j++)	
    {
	  /*    feedback section    */
    out=out-(long)((int)(((long)delay[1+(j*section)]*(long)(int)DEN[j][1] )>>15));

    delay[(j* section)]=(int)(out-(long)((int)(((long)delay[2+(j* section)]*(long)(int)DEN[j][2])>>15)));

	  /*    feedforward section   */
    out=(long)(delay[(j*section)]+(int)(((long)delay[1+(j* section)]*(long)(int)NUM[j][1])>>15));

    out=out+ (long)((int)(((long)delay[2+(j*section)]*(long)(int)NUM[j][2])>>15));		

	  /*    refresh signal buffer    */
    delay[2+(j* section)] = delay[1+(j* section)];
    delay[1+(j* section)] = delay[(j* section)];
    }       
    *output++ = (int)(out*8);	
  }
  return(TRUE);
}


/* Function for dataIO */

static void dataIO()
{
  return;
}