[Ether]

Let XU be the upper position limit.

Let XL be the lower position limit.

Let X be the current position, between those limits.

Let K be the size of the "speed zone" near either limit, where speed gets reduced.

Let J be the joystick command, between -1 and +1, where +1 commands a speed toward the upper limit.

Then:

if ( (X>XU-K) && (J>(XU-X)/K) ) J=(XU-X)/K;
else
if ( (X<XL+K) && (J<(XL-X)/K) ) J=(XL-X)/K;