On Tue, 2005-07-12 at 16:55 -0700, Andrew Morton wrote:
> Steven Rostedt <[email protected]> wrote:
> >
> > I will also admit that my ring buffers lost one byte per page. Because
> > I wanted to save on space with the accounting, and only had a start and
> > end pointer per page. So when start and end were equal, the buffer was
> > considered empty and when end was one less than start, it was considered
> > full. But since end always pointed to an empty spot, it would still be
> > empty when the buffer was full, thus wasting one byte per page. But to
> > solve this, I would either have to add another variable in the buffer
> > page descriptor (adding at least one byte, but probably 4 bytes) which
> > would just be more waste, or I would have to make a complex system even
> > more complex (ie. adding a flag on the end pointer at the MSB to
> > differentiate between end being empty or filled).
>
> Nope. Just make the indices 32-bit numbers and let them wrap.
>
> Full: (tail - head) == size
> Empty: (tail - head) == 0
> Add item: buf[head++ & (size-1)] = item;
> Remove item: buf[tail++ & (size-1)]
You know I knew someone would have an answer. Look for version 0.2.1
comming soon :-)
Thanks,
-- Steve
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