Counting Rotations on absolute encoder

Hello!

I am trying to count the number of rotations on an absolute encoder. I need to be able to count in both directions, so if the encoder spins forward, and then back, I would need the relative number of rotations from the starting position.

The encoder outputs and angle value from 0 to 255. I tried a set of if statments but the way I set it up was not logically sound.

How should I go about this?

function y = fcn(u)
% u is a value from 0 to 255
% y needs to be a value from 0 to 255 from x rotations of the encoder
c=0;
v=0;
if (u == 255) && (c==0)
    c=1;
elseif (u > 254) && (c==1)
    c=2;
elseif (u > 254) && (c==2)
    c=3;
elseif (u > 254) && (c==3)
    c=4;
x= 0.33;
z= u+c*255
y = x*z;