firfltr.c

TI的DSP C55X的应用程序

/**********************************************************************
*  firfltr.c - An FIR filter
*
*  Block diagram:
*           --------
*  x(n) --->| b(n) |---> y(n)
*           --------
*  where
*    x(n) is input signal
*    b(n) is impulse response (coefficients) of FIR filter
*    y(n) is filtered output
*
*  This program is executed by keying in the following command:
*
*    firfltr infile coefile outfile <enter>
*
*  where
*    infile is file name of input signal
*    coefile is file name of filter coefficients
*    outfile is file name output signal
*
**********************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define MAX  2048             /* maximum order of filter */

void main(int argc, char *argv[])
{
  void shift(float *, int, float);  /* function to update signal vector 
*/
  float fir(float *, float *, int); /* function to perform FIR 
filtering */

/*****************************************************************
*    Define and initialize variables
*****************************************************************/
  int len_imp = 0;            /* order of filter */
  float xn;                   /* x(n), input signal */
  float bn;                   /* b(n), filter coefficients */
  float yn;                   /* y(n), output signal */
  float bn_coef[MAX];         /* b(n) vector */
  float xn_buf[MAX];          /* x(n) vector */
  FILE  *fpin;                /* file pointer of x(n) */
  FILE  *fpimp;               /* file pointer of b(n) */
  FILE  *fpout;               /* file pointer of y(n) */

/*****************************************************************
*    Define usage of executable file
*****************************************************************/
  if (argc < 4)
  {
    fprintf(stderr,"Usage: firfltr infile coefile outfile<enter>\n");
    fprintf(stderr,"    infile is input file name\n");
    fprintf(stderr,"    coefile is coefficients file name\n");
    fprintf(stderr,"    outfile is output file name\n");
    exit(0);
  }
  if ((fpin = fopen(argv[1],"rb")) == NULL)  /* open input file */
  {
    fprintf(stderr,"Can't open input data file %s!\n",argv[1]);
    exit(0);
  }
  if ((fpimp = fopen(argv[2],"rb")) == NULL) /* open coefficients file 
*/
  {
    fprintf(stderr,"Can't open coefficients file %s!\n",argv[2]);
    exit(0);
  }
  fpout = fopen(argv[3],"wb");               /* open output file */
  while((fscanf(fpimp,"%f",&bn)) != EOF)
  {
    bn_coef[len_imp] = (float)bn;            /* read coefficients */
    xn_buf[len_imp] = 0.;                    /* clear x(n) vector */
    len_imp++;                               /* order of filter */
  }
/*****************************************************************
*  Filtering of x(n) by FIR filter b(n) to get y(n)
*****************************************************************/
while(fread(&xn, sizeof(float), 1, fpin) == 1)
  {
    shift(xn_buf, len_imp, xn);              /* update x(n) vector */
    yn = fir(xn_buf,bn_coef,len_imp);        /* FIR filtering */
    fwrite(&yn, sizeof(float), 1, fpout);    /* write output y(n) */
  }
  fcloseall();                               /* close all data files */
}

/*****************************************************************
*  SHIFT - This function updates signal vector of order N
*          data stored as [x(n)  x(n-1) ... x(n-N+1)]
*****************************************************************/
void  shift(float *x, int N, float new)
{
  int i;                      /* loop index */
  for (i=N-1; i>0; i--)  
  {
    x[i] = x[i-1];            /* shift old data x(n-i) */
  }
  x[0] = new;                 /* insert new data x(n) */
  return;
}

/*****************************************************************
*  FIR - This function performs FIR filtering (linear convolution)
*          ntap-1
*    y(n) = sum  hi * x(n-i)
*           i=0
*****************************************************************/
float fir(float *x, float *h, int ntap)
{
  float yn = 0.0;              /* output of FIR filter */
  int i;                       /* loop index */
  for (i=0; i<ntap; i++) 
  {
    yn += h[i]*x[i];           /* convolution of x(n) with h(n) */
  }
  return(yn);                  /* return y(n) to main function */
}