real_t_fft.c

基于c166的 FFT算法源程序

/******************************************************************************
*	Module:		main() 
*	Filename:	real_T_FFT.c 
*	Project:	DSP library for XC166 microcontroller
*------------------------------------------------------------------------------
*	Compiler:	Keil
*
*	Version:	V1.2
*
*	Description:
*				This example demonstrates the usage of the function 
*				real_T_FFT() which implements the real-valued forward 
*				Fast Fourie Transform (FFT) with decimation-in-time. 
*				The input values are real in 1Q15 format within [1,-1].
*
*	Usage:		To make the program runing, the following files are needed to
*				add into the project:
*					1. real_DIT_FFT.c  (forward Fourier transform) 
*					2. FloatTo1Q15.c (format change from floting to 1Q15)
*					3. Bit_reverse.c (bit reverse of the input indices)
*				   
*	References:	1. <C166S V2 User Manual>  
*
*	Date		May 2003
*				                              
*	Copyright:	Infineon Technologies AG         
******************************************************************************/

#include "DspLib_Keil.h"
#include <stdio.h>
#include <stdlib.h>


#define ABSVAL(A) ((A) >= 0 ? (A) : (-A))
#define MAXERROR	10

#define	N_x			16

//input data vector in 1Q15 format
DataS 	sdata x[N_x] ={
 21061,	/* 0 */  -3624,	/* 1 */    7564,	/* 2 */  19130,	/* 3 */  27641,	/* 4 */ 
 15609,	/* 5 */ -21215,	/* 6 */   -6180,	/* 7 */  28536,	/* 8 */  27319,	/* 9 */ 
 -5880,	/* 10 */ 25795,	/* 11 */ -28972,	/* 12 */ -9642,	/* 13 */ 20521,	/* 14 */ 
-32119,	/* 15 */ 
};

//reference output vector in 1Q15 format
DataS	sdata rtest[N_x+2] = {
     5347,      0,	  /*Re{X(0)}, Im{X(0)}*/	/* DC element */
	-2077,  -3242, 	  /*Re{X(1)}, Im{X(1)}*/
	  288,  -4611, 	  /*Re{X(2)}, Im{X(2)}*/
	-2424,   5522, 	  /*Re{X(3)}, Im{X(3)}*/
	 2954,  -1440, 	  /*Re{X(4)}, Im{X(4)}*/
	-3389,  -4056, 	  /*Re{X(5)}, Im{X(5)}*/
	 6077,  -4313, 	  /*Re{X(6)}, Im{X(6)}*/
	 6019,   1334, 	  /*Re{X(7)}, Im{X(7)}*/
	  810,      0,	  /*Re{X(8)}, Im{X(8)}*/ /* Nyquist point */
};
	   
float   Fdata [N_x];
DataS   Idata [N_x];
	//DataS 	i, exp;
   // DataS   X[N_x+2], table[3*N_x/4];
DataS	  table[3*N_x/4];
float	  Ftable[3*N_x/4];
  	//DataS   index[N_x/2];
	//float	y;

	//DataS	diff, errflag=0;
 
void main()
{
	DataS 	i, exp;
    DataS   X[N_x+2];// table[3*N_x/4];
  	DataS   index[N_x/2];
	float	y;

	DataS	diff, errflag=0;
	//float   Fdata [N_x];
	//DataS   Idata [N_x]; 
	for(i=0;i<N_x;i++)
    {  
     Fdata[i]=Q15toFloat(x[i]);
     Idata[i]=FloatTo1Q15(Fdata[i]);
    }

//generate trigonomic function table
 	for(i=0; i<3*N_x/4; i++)
 	{
		if(i<=N_x/2)
		{//change the format from floating to 1Q15
			y = FloatTo1Q15(2.*i/N_x);
 			table[i] = Sine(y);
			Ftable[i]=Q15toFloat(table[i]);
		}
		else
		{//change the format from floating to 1Q15
			y = FloatTo1Q15(2.*(i-N_x)/N_x);
 			table[i] = Sine(y);
			Ftable[i]=Q15toFloat(table[i]);
		}
  	}
  
//generate the reverse index table
	for(i=0; i<N_x/2; i++)
		index[i] = i;

	exp = Bit_reverse(index, N_x/2);
	exp = exp+1;  //N_x = 2^exp

	// To point to the memory address, it needed to multiplay the indices by 4
	for(i=0; i<N_x/2; i++)
		index[i] = index[i] * 4; 

/************ Perform the Fourier Transform *************/

//call real_DIT_FFT routine to perform real forward Fourier Transform 
 	real_DIT_FFT(x, index, exp, table, X);

/*------ test the function ------*/
//print the results, reference results and their difference
//the difference should be less than 10.
	for(i=0; i<N_x+2; i++)
	{
	   	diff = rtest[i] - X[i];	
		if(ABSVAL(diff) > MAXERROR)
			errflag = -1;
		printf("Y[%d] = %6d, %6d, %6d\n", i, X[i], rtest[i], ABSVAL(diff));
	
	}

    if(errflag == -1)
		printf("\nTest result: error \n");
	else
	    printf("\nTest result: ok\n");
	 
}		 

// End of file