spline (NR in C) in C#

static void spline(float[] x, float[] y, int n, float ld, bool lnat, float rd, bool rnat, float[] y2)
{
    int i, k;
    float p, qn, sig, un;
    float[] u = new float[n];
    if (lnat)
        y2[0] = u[0] = 0.0f;
    else {
        y2[0] = -0.5f;
        u[0] = (3.0f / (x[1] - x[0])) * ((y[1] - y[0]) / (x[1] - x[0]) - ld);
    }
    for (i = 1; i < n - 1; ++i) {
        sig = (x[i] - x[i - 1]) / (x[i + 1] - x[i - 1]);
        p = sig * y2[i - 1] + 2.0f;
        y2[i] = (sig - 1.0f) / p;
        u[i] = (y[i + 1] - y[i]) / (x[i + 1] - x[i]) - (y[i] - y[i - 1]) / (x[i] - x[i - 1]);
        u[i] = (6.0f * u[i] / (x[i + 1] - x[i - 1]) - sig * u[i - 1]) / p;
    }
    if (rnat)
        qn = un = 0.0f;
    else {
        qn = 0.5f;
        un = (3.0f / (x[n - 1] - x[n - 2])) * (rd - (y[n - 1] - y[n - 2]) / (x[n - 1] - x[n - 2]));
    }
    y2[n - 1] = (un - qn * u[n - 2]) / (qn * y2[n - 2] + 1.0f);
    for (k = n - 2; k >= 0; --k)
        y2[k] = y2[k] * y2[k + 1] + u[k];
}