float SquaredDistancePointSolidBox (Box box, Point P)
{
    D = P - box.C;
    sqrDist = 0;

    for (i = 0; i <= 2; i++)
    {
        s[i] = Dot(box.U[i],D);
        if ( s[i] < -box.e[i] )
        {
            delta = s[i] + box.e[i];
            sqrDist += delta*delta;
            s[i] = -box.e[i];  // include only if you want closest point
        }
        else if ( s[i] > box.e[i] )
        {
            delta = s[i] - box.e[i];
            sqrDist += delta*delta;
            s[i] = box.e[i];   // include only if you want closest point
        }
    }

    // closest point is C + sum_{i=0}^2 s[i]*box.U[i]
    return sqrDist;
}