process.c

来自「TMS320LF2407 教程 例子 英文 TI」· C语言 代码 · 共 98 行

/*FFT.C-FFT RADIX-2 USING DIF. FOR UP TO 512 POINTS       */

#include "fftcmplx.h"  /*complex structure definition      */
#include "twid256.h"   /*header file with twiddle constants*/


void FFT(COMPLEX *Y, int N) /*input sample array, # of points      */
  {
  COMPLEX temp1,temp2;      /*temporary storage variables          */
  int i,j,k;                /*loop counter variables               */
  int upper_leg, lower_leg; /*index of upper/lower butterfly leg   */
  int leg_diff;             /*difference between upper/lower leg   */
  int num_stages=0;         /*number of FFT stages, or iterations  */
  int index, step;          /*index and step between twiddle factor*/

/* log(base 2) of # of points = # of stages  */
  i=1;
  do
	 {
	 num_stages+=1;
	 i = i *2 ;         
	 } while (i!=N);

/* starting difference between upper and lower butterfly legs*/
  leg_diff = N/2;

  /* step between values in twiddle factor array twiddle.h     */
  step = 512 / N;

  /* For N-point FFT                                           */

  for (i=0;i<num_stages;i++)
	 {
	 index=0;
	 for (j=0;j<leg_diff;j++)
		{
		for (upper_leg=j;upper_leg<N;upper_leg+=(2*leg_diff))
		  {
		  lower_leg = upper_leg + leg_diff;
		  temp1.real=(Y[upper_leg]).real + (Y[lower_leg]).real;
		  temp1.imag=(Y[upper_leg]).imag + (Y[lower_leg]).imag;
		  temp2.real=(Y[upper_leg]).real - (Y[lower_leg]).real;
		  temp2.imag=(Y[upper_leg]).imag - (Y[lower_leg]).imag;

		  (Y[lower_leg]).real =  ((long)temp2.real * (w[index]).real)/8192;
		  (Y[lower_leg]).real -= ((long)temp2.imag * (w[index]).imag)/8192;

		  (Y[lower_leg]).imag = ((long)temp2.real * (w[index]).imag)/8192;
		  (Y[lower_leg]).imag += ((long)temp2.imag * (w[index]).real)/8192;

		  (Y[upper_leg]).real = temp1.real;

		  (Y[upper_leg]).imag = temp1.imag;
		  }
		index+=step;
		}
	 leg_diff=leg_diff / 2;
	 step *= 2;  
	 }
/* bit reversal for resequencing data */
  j=0;
  for (i=1;i<(N-1);i++)
	 {
	 k = N/2;
	 while (k<=j)
		{
		j=j-k;
		k >>= 1;
		}
	 j=j+k;
	 if (i<j)
		{
		temp1.real =  (Y[j]).real;
		temp1.imag =  (Y[j]).imag;
		(Y[j]).real = (Y[i]).real;
		(Y[j]).imag = (Y[i]).imag;
		(Y[i]).real = temp1.real;
		(Y[i]).imag = temp1.imag;
		}
	 }
  return;
  }