Messages in this thread | | | Date | Thu, 16 Sep 2004 00:04:38 -0700 | From | Andrew Morton <> | Subject | Re: [RFC, 2.6] a simple FIFO implementation |
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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... - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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