Documentation

Counter is a class that composes multiple counters into a single one. It is similar to odometers found in olds cars, once all counters reach their maximum they reset to zero - i.e. odometer rollover. See countSucc and countPred for API usage examples.

Example use case: when driving a monitor through VGA you would like to keep track at least two counters: one counting a horizontal position, and one vertical. Perhaps a fancy VGA driver would also like to keep track of the number of drawn frames. To do so, the three counters are setup with different types. On each round of the horizontal counter the vertical counter should be increased. On each round of the vertical counter the frame counter should be increased. With this class you could simply use the type:

(FrameCount, VerticalCount, HorizontalCount)

and have countSucc work as described.

NB: This class exposes four functions countMin, countMax, countSuccOverflow, and countPredOverflow. These functions are considered an internal API. Users are encouraged to use countSucc and countPred.

Successor of a counter.

Examples:

>>> type T = (Unsigned 2, Unsigned 2)
>>> countSucc @T (1, 1)
(1,2)
>>> countSucc @T (1, 2)
(1,3)
>>> countSucc @T (1, 3)
(2,0)
>>> countSucc @T (3, 3)
(0,0)
>>> countSucc @(Index 9, Index 2) (0, 1)
(1,0)
>>> countSucc @(Either (Index 9) (Index 9)) (Left 8)
Right 0

Predecessor of a counter

Examples:

>>> type T = (Unsigned 2, Unsigned 2)
>>> countPred @T (1, 2)
(1,1)
>>> countPred @T (1, 3)
(1,2)
>>> countPred @T (2, 0)
(1,3)
>>> countPred @T (0, 0)
(3,3)
>>> countPred @(Index 9, Index 2) (1, 0)
(0,1)
>>> countPred @(Either (Index 9) (Index 9)) (Right 0)
Left 8