yzgfft.txt

我自己的FFT算法

bool FFT(double *fr,double *fi,int n,bool flag)
{
	int mp,arg,cntr,p1,p2;
	int i,j,a,b,k;
	double sign,pr,ppi,harm,t;
	double *ca,*sa;
	ca=(double *) calloc(n,sizeof(double));
	sa=(double *) calloc(n,sizeof(double));
	if(ca==NULL || sa==NULL)
		return false;
	j=0;
	if(flag)
	{
		sign=1.0;
		for(i=0;i<=n-1;++i)
		{
			fr[i]=fr[i]/n;
			fi[i]=fi[i]/n;
		}
	}
	else
		sign=-1.0;
	for (i=0;i<=n-2;++i)
	{
		if (i<j)
		{
			t=fr[i];
			fr[i]=fr[j];
			fr[j]=t;
			t=fi[i];
			fi[i]=fi[j];
			fi[j]=t;
		}
		k=n/2;
		while (k<=j)
		{
			j-=k;
			k/=2;
		}
		j+=k;
	}
	mp=0;
	i=n;
	while (i!=1)
	{
		mp+=1;
		i/=2;
	}
	harm=2*M_PI/n;
	for (i=0;i<=n-1;++i)
	{
		sa[i]=sign*sin(harm*i);
		ca[i]=cos(harm*i);
	}
	a=2;
	b=1;
	for (cntr=1;cntr<=mp;++cntr)
	{
		p1=n/a;
		p2=0;
		for (k=0;k<=b-1;++k)
		{
			i=k;
			while (i<n)
			{
				arg=i+b;
				if(k==0)
				{
					pr=fr[arg];
					ppi=fi[arg];
				}
				else
				{
					pr=fr[arg]*ca[p2]-fi[arg]*sa[p2];
					ppi=fr[arg]*sa[p2]+fi[arg]*ca[p2];
				}
				fr[arg]=fr[i]-pr;
				fi[arg]=fi[i]-ppi;
				fr[i]+=pr;
				fi[i]+=ppi;
				i+=a;
			}
			p2+=p1;;
		}
		a*=2;
		b*=2;
	}
	free(ca);
	free(sa);
	return true;
}