Zrealft.cin

// zrealft.cin is C++ routine required for compilation of examples with DCTI, Discrete Cosine transform of the First kind.

void zrealft(z_type data[], unsigned long n, int isign) { /* void zfour1(z_type data[], unsigned long nn, int isign);*/ unsigned long i,i1,i2,i3,i4,np3; z_type c1=0.5,c2,h1r,h1i,h2r,h2i; double wr,wi,wpr,wpi,wtemp,theta; theta=M_PI/(double) (n>>1); if(isign == 1){ c2 = -(double)0.5; zfour1(data,n>>1,1);} else { c2 = (double)0.5; theta = -theta; } wtemp=sin((double)0.5*theta); wpr = -(double)2.0*wtemp*wtemp; wpi=sin(theta); wr=(double)1.0+wpr; wi=wpi; np3=n+3; for(i=2;i<=(n>>2);i++) { i4=1+(i3=np3-(i2=1+(i1=i+i-1))); h1r=c1*(data[i1]+data[i3]); h1i=c1*(data[i2]-data[i4]); h2r = -c2*(data[i2]+data[i4]); h2i=c2*(data[i1]-data[i3]); data[i1]=h1r+wr*h2r-wi*h2i; data[i2]=h1i+wr*h2i+wi*h2r; data[i3]=h1r-wr*h2r+wi*h2i; data[i4] = -h1i+wr*h2i+wi*h2r; wr=(wtemp=wr)*wpr-wi*wpi+wr; wi=wi*wpr+wtemp*wpi+wi; } if (isign == 1){ data[1] = (h1r=data[1])+data[2]; data[2] = h1r-data[2]; } else { data[1]=c1*((h1r=data[1])+data[2]); data[2]=c1*(h1r-data[2]); zfour1(data,n>>1,-1); } }