Comparing head/tail indexes cannot distinguish between empty/full cases,
so we end up wasting one item in the circular buffer. This also limits
the smallest and efficient size choice to be 4.
If the circular buffer is large, there's no issue, however for the
motion planner the block size is significant, and I was planning to use
exactly a ring buffer of two: one busy block, plus one planned.
Modify the indexer to store the internal "index" (aka cursor) pointer to
be one extra bit deeper than the final index. Comparing the underlying
cursor allow to distinguish the empty/full case due to the extra bit,
while producing the final index requires simple masking.
This is just as efficient if the size is a power of two with
2-complement wrap-around logic, which is the optimized case. However
the implementation also works for non-power-of-two sizes.
Add tests for more failure cases in the CircularBuffer which is built on
top.
(tecnique described in the Art of Computer Programming by Knuth)
Yuri D'Elia
D.R.racer