iir2.c

用dsp解压mp3程序的算法

/*****************************************************************
*  iir2.c - C program for first-order IIR filtering
******************************************************************
*  System configuration:
*
* 
*  x(n) |----------------| y(n)
*  ---->| Lowpass filter |----->
*       |----------------|
*
******************************************************************
*  System simulation configuration:
*
*     x(n) is the input data from data file "xn.dat"
*     y(n) is the output data to data file "yn.dat"
*
*****************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/*Global declaration */
int in_buffer[100];
int out_buffer[100];
#define TRUE 1

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


/*----- Main program ----- */
void main()
{

/*****************************************************************
*    Declare file pointers
*****************************************************************/

  int *input = &in_buffer[0];    /* input pointer               */
  int *output = &out_buffer[0];  /* output pointer              */

/*****************************************************************
*    Start of main program
*****************************************************************/

  while(TRUE)
  {           /* read in x(n) from data file and processing it  */

    /*************************************************************
    *    IIR filtering:
    *         y(n) = (1-alpha)*y(n-1)+alpha*x(n)
    *************************************************************/
    
	/* Read using Probe Point connected to a host file.     */
	dataIO(); 

	processing(input, output); 
  }
}

/* function for signal processing */
static int processing(int *input, int *output)
{
  int size = 100;
  float yn = 0.0;             /* y(n), output from IIR filter   */
  float alpha = 0.25;         /* alpha = 0.25                   */
  float alpha1 = 0.75;        /* alpha1 = 1 - alpha = 0.75      */

  while(size--){              /* *output++ = *input++*0.5;      */
	
    *output = (int)((alpha1*yn + alpha*((float)*input++))+0.5);
    yn = (float)*output++;   
  }
  return(TRUE);
}


/* dataIO - function for data I/O  */

static void dataIO ()
{
  return;
}