kfft.c

DSP TMS320vc5416 FFT代码

	#include "math.h"
void kfft(pr,pi,n,k,fr,fi,l,il)
	int n,k,l,il;
double pr[],pi[],fr[],fi[];
{ 
	int it,m,is,i,j,nv,l0;
	double p,q,s,vr,vi,poddr,poddi;
	
	for (it=0; it<=n-1; it++)
	{ 
		m=it; 
		is=0;
		for (i=0; i<=k-1; i++)
		{ 
			j=m/2; 
			is=2*is+(m-2*j); 
			m=j;
		}
		fr[it]=pr[is]; 
		fi[it]=pi[is];

	}

	pr[0]=1.0; 
	pi[0]=0.0;
	p=6.283185306/(1.0*n);		// 3.1415926
	pr[1]=cos(p); 
	pi[1]=-sin(p);
	if (l!=0) 
		pi[1]=-pi[1];
	for (i=2; i<=n-1; i++)
	{ 
		p=pr[i-1]*pr[1]; 
		q=pi[i-1]*pi[1];
		s=(pr[i-1]+pi[i-1])*(pr[1]+pi[1]);
		pr[i]=p-q; 
		pi[i]=s-p-q;
	}

	for (it=0; it<=n-2; it=it+2)
	{ 
		vr=fr[it]; 
		vi=fi[it];
		fr[it]=vr+fr[it+1]; 
		fi[it]=vi+fi[it+1];
		fr[it+1]=vr-fr[it+1]; 
		fi[it+1]=vi-fi[it+1];
	}
	m=n/2; 
	nv=2;
	for (l0=k-2; l0>=0; l0--)
	{ 
		m=m/2; 
		nv=2*nv;
		for (it=0; it<=(m-1)*nv; it=it+nv)
			for (j=0; j<=(nv/2)-1; j++)
			{ 
				p=pr[m*j]*fr[it+j+nv/2];
				q=pi[m*j]*fi[it+j+nv/2];
				s=pr[m*j]+pi[m*j];
				s=s*(fr[it+j+nv/2]+fi[it+j+nv/2]);
				poddr=p-q; poddi=s-p-q;
				fr[it+j+nv/2]=fr[it+j]-poddr;
				fi[it+j+nv/2]=fi[it+j]-poddi;
				fr[it+j]=fr[it+j]+poddr;
				fi[it+j]=fi[it+j]+poddi;
			}
		}
	if (l!=0)
		for (i=0; i<=n-1; i++)
		{ 
			fr[i]=fr[i]/(1.0*n);
			fi[i]=fi[i]/(1.0*n);
		}
	if (il!=0)
		for (i=0; i<=n-1; i++)
		{ 
			pr[i]=sqrt(fr[i]*fr[i]+fi[i]*fi[i]);
			if (fabs(fr[i])<0.000001*fabs(fi[i]))
			{ 
				if ((fi[i]*fr[i])>0) 
					pi[i]=90.0;
				else 
					pi[i]=-90.0;
			}
			else
				pi[i]=atan(fi[i]/fr[i])*360.0/6.283185306;
		}
		
	return;
	
  }