Test overflow and underflow
For data pointer and data itself

+>
--
++

>+>++>+[->+++[-<++++>]<<]>

<<<<<<<<<<<<
>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]
<<<<<<<<<<<<

-[--->+<]>------.[------->+++<]>.[->++++++++++<]>.>++++++++++.