public LSL_Float llAngleBetween(LSL_Rotation a, LSL_Rotation b)
{
if (!ScriptProtection.CheckThreatLevel(ThreatLevel.None, "LSL", m_host, "LSL", m_itemID)) return new LSL_Float();
double aa = (a.x * a.x + a.y * a.y + a.z * a.z + a.s * a.s);
double bb = (b.x * b.x + b.y * b.y + b.z * b.z + b.s * b.s);
double aa_bb = aa * bb;
if (aa_bb == 0) return 0.0;
double ab = (a.x * b.x + a.y * b.y + a.z * b.z + a.s * b.s);
double quotient = (ab * ab) / aa_bb;
if (quotient >= 1.0) return 0.0;
return Math.Acos(2 * quotient - 1);
}