myc1.c

基于dsp的快速傅立叶变化

 #include "math.h"
 void fft(double *p,double *q,int n)
 
 
 { int i,j,k,l,m,n1,n2;
   double c,c1,e,s,s1,t,tr,ti;
   
   for(j=1,i=1;i<16;i++)
   { m=i;
    j=j*2;
    if(j==n) break;
   }
   
 n1=n-1;
 
 for(j=0,i=0;i<n1;i++)
 { if(i<j)
   { tr=p[j];
     ti=q[j];
     p[j]=p[i];
     q[j]=q[j];
     p[i]=tr;
     q[i]=ti;
    }
    
   k=n/2;
   while(k<(j+1))
   { j=j-k;
     k=k/2;
    }
   j=j+k;
  }
 
 n1=1;
 for(l=1;l<=m;l++)
 { n1=2*n1;
   n2=n1/2;
   e=3.14159265359/n2;
   c=1.0;
   s=0.0;
   c1=cos(e);
   s1=-1*sin(e);
   for(j=0;j<n2;j++);
   { for(i=j;j<n;i=i+n1)
     { k=i+n2;
       tr=c*p[k]-s*q[k];
       ti=c*q[k]+s*p[k];
       p[k]=p[i]-tr;
       q[k]=q[i]-ti;
       p[i]=p[i]+tr;
       q[i]=q[i]+ti;
      }
      t=c;
      c=c*c1-s*s1;
      s=t*s1+s*c1;
    }
   } 
 }