kfft.cpp

超级精简版本的傅里叶变换

#include "math.h"

kfft(pr,pi,n, k,fr,fi,l,il)



void kfft(float *pr,float *pi,int n,int k,float *fr,float *fi,int l,int il)
  {
	int it,m,is,i,j,nv,l0;
    float 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);
    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;
	  }
  }