Update softening.h

Author: TimGoTheCreator

src/dt/softening.h

@@ -11,6 +11,7 @@
 
 #pragma once
 #include <cmath>
+#include "floatdef.h"
 
 /* Softening for BarnesHut */
 inline real nextSoftening(real nodeSize,
@@ -53,4 +54,4 @@ inline real pairSoftening(real ma, real mb)
         eps = eps_min;
 
     return eps; // return epsilon
-}
+}