+ /* we need to do this for the subspline between [start,end], not [0,1]
+ as a transformation of t->a*t+b does nothing to highest coefficient
+ of the spline except multiply it with a^3, we just need to modify
+ d here. */
+ {double m = end-start;
+ dx*=m*m*m;
+ dy*=m*m*m;
+ }
+