fft.rar_fft

//l=0时，pr存放采样输入的实部，返回离散傅立叶变换的模；l=1时，pr存放傅立叶变换的实部，返回逆傅立叶变换的模 //l=0时，pi存放采样输入的虚部，返回离散傅立叶变换的幅角；l=1时，pi存放傅立叶变换的虚部，返回逆傅立叶变换的幅角 //l=0时，fr返回傅立叶变换的实部;l=1时返回逆傅立叶变换的实部 //l=0时，fi返回傅立叶变换的虚部;l=1时返回逆傅立叶变换的虚部 (l=0时正变换，l=1时逆变换) //il=0时，表示不要求本函数计算傅立叶变换或逆傅立叶变换的模或幅角 //il=1时，表示要求本函数计算傅立叶变换或逆傅立叶变换的模或幅角 #include <math.h> //快速傅立叶变换子程序 void kfft(pr, pi, n, k, fr, fi, l, il) int n, k, l, il; float pr[], pi[], fr[], fi[]; { int it, m, is, i, j, nv, l0; float p, q, s, vr, vi, poddr, poddi; for (it = 0; it < n; it++) { m = it; is = 0; for (i = 0; i < k; 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; 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; 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*nv;it = it+nv) for (j = 0; j < nv/2; 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; i++) { fr[i] = fr[i]/(1.0*n); fi[i] = fi[i]/(1.0*n); } if (il != 0) for (i = 0; i < n; 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; }