fft.c

基于TMS320C5416平台的谱分析程序

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/*                                                                           */
/* FILENAME                                                                  */
/* 	 fft.c                                                                   */
/*                                                                           */
/* DESCRIPTION                                                               */
/*   Fast Fourier Transform for up to 256 points.                            */
/*                                                                           */
/*   Here N is the number of FFT terms and Fs is the sampling frequency of   */
/*   48000 Hz.                                                               */ 
/*                                                                           */
/* REVISION                                                                  */
/*   Revision: 1.00	                                                         */
/*   Author  : Richard Sikora                                                */
/*---------------------------------------------------------------------------*/
/*                                                                           */
/* HISTORY                                                                   */
/*   Revision 1.00                                                           */
/*   2nd November 2002. Created by Richard Sikora from TMS320C5402 code.     */
/*                                                                           */
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/*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, number 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;
  }

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/* End of fft.c                                                              */
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