/**
* Links the user-supplied input sequence and output transform arrays. Propagates the links to
* child DFTs.
*
* @param xr double[] containing the input sequence real part.
* @param xi double[] containing the input sequence imaginary part.
* @param Xr double[] containing the output sequence real part.
* @param Xi double[] containing the output sequence imaginary part.
*/
void link(double[] xr, double[] xi, double[] Xr, double[] Xi) {
this.xr = xr;
this.xi = xi;
this.Xr = Xr;
this.Xi = Xi;
dft1.link(xr, xi, Xr, Xi);
dft2.link(xr, xi, Xr, Xi);
dft3.link(xr, xi, Xr, Xi);
}
/** Evaluates the complex DFT. */
void evaluate() {
double T1r, T1i, T3r, T3i;
double Rr, Ri, Sr, Si;
double Wr, Wi;
dft1.evaluate();
dft2.evaluate();
dft3.evaluate();
// k = 0 butterfly
int kp = Xoffset;
int kpN4 = kp + N4;
int kpN2 = kpN4 + N4;
int kp3N4 = kpN2 + N4;
Rr = Xr[kpN2] + Xr[kp3N4];
Ri = Xi[kpN2] + Xi[kp3N4];
Sr = Xi[kp3N4] - Xi[kpN2];
Si = Xr[kpN2] - Xr[kp3N4];
Xr[kpN2] = Xr[kp] - Rr;
Xi[kpN2] = Xi[kp] - Ri;
Xr[kp3N4] = Xr[kpN4] + Sr;
Xi[kp3N4] = Xi[kpN4] + Si;
Xr[kp] += Rr;
Xi[kp] += Ri;
Xr[kpN4] -= Sr;
Xi[kpN4] -= Si;
// k = 1 through N8-1 butterflies
int fk;
for (int k = 1; k < N8; k++) {
fk = f * k;
kp = k + Xoffset;
kpN4 = kp + N4;
kpN2 = kpN4 + N4;
kp3N4 = kpN2 + N4;
// T1 = Wk*O1
// T3 = W3k*O3
Wr = c[fk];
Wi = s[fk];
T1r = Wr * Xr[kpN2] - Wi * Xi[kpN2];
T1i = Wr * Xi[kpN2] + Wi * Xr[kpN2];
Wr = c3[fk];
Wi = s3[fk];
T3r = Wr * Xr[kp3N4] - Wi * Xi[kp3N4];
T3i = Wr * Xi[kp3N4] + Wi * Xr[kp3N4];
// R = T1 + T3
// S = i*(T1 - T3)
Rr = T1r + T3r;
Ri = T1i + T3i;
Sr = T3i - T1i;
Si = T1r - T3r;
Xr[kpN2] = Xr[kp] - Rr;
Xi[kpN2] = Xi[kp] - Ri;
Xr[kp3N4] = Xr[kpN4] + Sr;
Xi[kp3N4] = Xi[kpN4] + Si;
Xr[kp] += Rr;
Xi[kp] += Ri;
Xr[kpN4] -= Sr;
Xi[kpN4] -= Si;
}
// k = N/8 butterfly
kp = N8 + Xoffset;
kpN4 = kp + N4;
kpN2 = kpN4 + N4;
kp3N4 = kpN2 + N4;
// T1 = Wk*O1
// T3 = W3k*O3
T1r = SQRT2BY2 * (Xr[kpN2] + Xi[kpN2]);
T1i = SQRT2BY2 * (Xi[kpN2] - Xr[kpN2]);
T3r = SQRT2BY2 * (Xi[kp3N4] - Xr[kp3N4]);
T3i = -SQRT2BY2 * (Xi[kp3N4] + Xr[kp3N4]);
// R = T1 + T3
// S = i*(T1 - T3)
Rr = T1r + T3r;
Ri = T1i + T3i;
Sr = T3i - T1i;
Si = T1r - T3r;
Xr[kpN2] = Xr[kp] - Rr;
Xi[kpN2] = Xi[kp] - Ri;
Xr[kp3N4] = Xr[kpN4] + Sr;
Xi[kp3N4] = Xi[kpN4] + Si;
Xr[kp] += Rr;
Xi[kp] += Ri;
Xr[kpN4] -= Sr;
Xi[kpN4] -= Si;
// k = N/8+1 through N/4-1 butterflies
for (int k = N8 + 1; k < N4; k++) {
fk = reflect - f * k;
kp = k + Xoffset;
kpN4 = kp + N4;
kpN2 = kpN4 + N4;
kp3N4 = kpN2 + N4;
// T1 = Wk*O1
// T3 = W3k*O3
Wr = -s[fk];
Wi = -c[fk];
T1r = Wr * Xr[kpN2] - Wi * Xi[kpN2];
T1i = Wr * Xi[kpN2] + Wi * Xr[kpN2];
Wr = s3[fk];
Wi = c3[fk];
T3r = Wr * Xr[kp3N4] - Wi * Xi[kp3N4];
T3i = Wr * Xi[kp3N4] + Wi * Xr[kp3N4];
// R = T1 + T3
// S = i*(T1 - T3)
Rr = T1r + T3r;
Ri = T1i + T3i;
Sr = T3i - T1i;
Si = T1r - T3r;
Xr[kpN2] = Xr[kp] - Rr;
Xi[kpN2] = Xi[kp] - Ri;
Xr[kp3N4] = Xr[kpN4] + Sr;
Xi[kp3N4] = Xi[kpN4] + Si;
Xr[kp] += Rr;
Xi[kp] += Ri;
Xr[kpN4] -= Sr;
Xi[kpN4] -= Si;
}
}