iir1fx.c

用dsp解压mp3程序的算法

/*****************************************************************
*  iir1fx.c - C program for first-order IIR filtering using
*             fixed-point C code
*****************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void main()
{
  /***************************************************************
  *    Define variable arrays, define and clear variables
  ***************************************************************/
  int xn = 0;                /* x(n) from xn.dat file           */
  long yn = 0;               /* float yn = 0.0;                 */
  int alpha = 8192;          /* alpha = 0.25*32768              */
  int alpha1 = 24576;        /* alpha1 = 1 - alpha = 0.75*32768 */

  /***************************************************************
  *    Declare file pointers
  ***************************************************************/
  FILE *xn_in;                    /* file pointer of x(n)       */
  FILE *yn_out;                   /* file pointer of y(n)       */
  xn_in = fopen("xn.dat","r");    /* open file for input x(n)   */
  yn_out = fopen("yn.dat","w");   /* open file for output y(n)  */

  /***************************************************************
  *    Start of main program
  ***************************************************************/
  while( (fscanf(xn_in,"%d",&xn)) != EOF)
  {           /* read in x(n) from data file and processing it  */
    /*************************************************************
    *    IIR filtering:
    *         y(n) = (1-alpha)*y(n-1)+alpha*x(n)
    *************************************************************/
    /*yn = alpha1*yn+ alpha*(float)xn; */
    yn = (((long)(int)alpha1*(long)(int)yn)>>15)
        +(((long)(int)alpha*(long)(int)xn)>>15);
    fprintf(yn_out,"%d\n",(int)(yn));
        /* rounding y(n) to integer and write it to output file */
  }
  printf("Finish");
  fclose(xn_in);
  fclose(yn_out);                     /* close all opened files */
}