A bitmaks and binary tests are just the idea of compressing a bunch of small width data (usually booleans, ie 1 bit values) into a byte. So for instance we might use a bit field to represent which external walls of a rectangle in a spreadsheet get colored in and which internal lines get colored in:

Bit 7 : reserved
    6 : reserved
    5 : inside horiz
    4 : inside vert
    3 : bottom
    2 : top 
    1 : right 
    0 : left
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So a value of 255 corresponds to all sides being colored in. A value of 3 means just the left and right, a value of 5 is the top and left etc...

--- demerphq
my friends call me, usually because I'm late....