HP 50g: Neighbour Function (Dedekind Cut) Programme Challenge

[David Hayden]

Slow and simple, but it works. This just keeps adding or subtracting 10^n for successively larger values of n until X+10^n changes.

Code:

@ NEIGHBOR
@ Given X & Y (X on lvl2, Y on lvl1), find the next
@ number to X in the direction of Y that the calc can
@ represent.  If X=Y then return X
«
OVER - SIGN  @ X (-1,0,1)
1E-499 *
IF DUP THEN  @ Special case for X==Y
    WHILE DUP2 + PICK3 ==
    REPEAT
       10. *
    END
END
+
»