/*****************fft programe*********************/
#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 ;
}

/*****************main programe********************/

#include<math.h>
#include<stdio.h>
#include<stdlib.h>
#include "typedef.h"

float result[257];
struct compx s[257];
int Num=256 ;
const float pp=3.14159 ;

main()
{
    int i=1 ;
    for(;i<0x101;i++)
    {
        s[i].real=sin(pp*i/32);
        s[i].imag=0 ;
    }
   
    FFT(s,Num);
   
    for(i=1;i<0x101;i++)
    {
        result[i]=sqrt(pow(s[i].real,2)+pow(s[i].imag,2));
    }
}

评论