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Stelian Pop <stelian@popies.net> wrote:
>
> > Implementation-wise, the head and tail indices should *not* be constrained
> > to be less than the size of the buffer. They should be allowed to wrap all
> > the way back to zero. This allows you to distinguish between the
> > completely-empty and completely-full states while using 100% of the storage.
>
> Do you mean 'size' (the size of alloc'ed buffer) is redundant or 'len'
> (the amount of data in the FIFO) is redundant ? I see how 'len' could
> be removed (and didn't do it in the first place because I choosed
> code simplification over a 4 bytes gain in storage), but I hardly
> see how 'size' could be removed...
Well I'm not sure what the semantic difference is between `size' and `len'.
They're not very well-chosen identifiers, really.
My point is that there is no need to store the "number of bytes currently
in the buffer", because that is always equal to `head - tail' if you allow
those indices to freely wrap.
All the struct needs is `head', `tail' and `number_of_bytes_at_buf', all
unsigned.
add(char c)
{
p->buf[p->head++ % p->number_of_bytes_at_buf] = c;
}
get()
{
return p->buf[p->tail++ % p->number_of_bytes_at_buf];
}
free_space()
{
return p->head - p->tail;
}
pretty simple...
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