add orbitClampAngle function

src/orbits.cpp

@@ -253,3 +253,13 @@ getPropagatedTrueAnomaly(system_2body sys,
 	return getTrueAnomFromEccAnom(sys.ep.e, ecc_anom);
 }
 
+
+// FIXME: organize into interface/internal functions
+
+// NOTE: return an equivalent angle between 0 and 2 pi radians
+double
+orbitClampAngle(double theta)
+{
+	double revs = floor(theta / (2 * M_PI));
+	return theta - revs * 2 * M_PI;
+}