fft.c

TMS320VC5402 DSK的例程

#include "typedef.h"
#include "math.h"

struct compx EE(struct compx b1,struct compx b2)
{
struct compx b3;
b3.real=b1.real*b2.real-b1.imag*b2.imag;
b3.imag=b1.real*b2.imag+b1.imag*b2.real;
return(b3);
}

void FFT(struct compx *xin,int N)
{
int f,m,nv2,nm1,i,k,j=1,l;
/*int f,m,nv2,nm1,i,k,j=N/2,l;*/
struct compx v,w,t;
nv2=N/2;
f=N;
for(m=1;(f=f/2)!=1;m++){;}
nm1=N-1;    

/*变址运算*/
for(i=1;i<=nm1;i++)
{
	if(i<j){t=xin[j];xin[j]=xin[i];xin[i]=t;}
	k=nv2;
	while(k<j){j=j-k;k=k/2;}
	j=j+k;
}

{
int le,lei,ip;
float pi;
for(l=1;l<=m;l++)
{   le=pow(2,l);// 这里用的是L而不是1  !!!!
    lei =le/2;
	pi=3.14159;
	v.real=1.0;
	v.imag=0.0;  
	w.real=cos(pi/lei);
	w.imag=-sin(pi/lei);
	for(j=1;j<=lei;j++)
	{
		/*double p=pow(2,m-l)*j;
		double ps=2*pi/N*p;
		w.real=cos(ps);
		w.imag=-sin(ps);*/
	for(i=j;i<=N;i=i+le)
	{ /*  w.real=cos(ps);
		w.imag=-sin(ps);*/
		ip=i+lei;
	    t=EE(xin[ip],v);
		xin[ip].real=xin[i].real-t.real;
		xin[ip].imag=xin[i].imag-t.imag;
		xin[i].real=xin[i].real+t.real;
		xin[i].imag=xin[i].imag+t.imag;
	}
	v=EE(v,w);
	}
}
}   
return;
}