Messages in this thread | | | Date | Fri, 17 Sep 2004 12:32:07 +0200 | From | Stelian Pop <> | Subject | Re: [RFC, 2.6] a simple FIFO implementation |
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On Fri, Sep 17, 2004 at 11:00:22AM +1000, Peter Chubb wrote:
> Andrew> All the struct needs is `head', `tail' and > Andrew> `number_of_bytes_at_buf', all unsigned. > > Andrew> add(char c) { > Andrew> p-> buf[p->head++ % p->number_of_bytes_at_buf] = c; > Andrew> } > > This depends on how expensive % is. On IA64, something like this: > > add(char c) { > int i = p->head == p->len ? p->head++ : 0; > p->buf[i] = c; > } > > is cheaper, as % generates a subroutine call to __modsi3. It also is > shorter =-- 12 bundles as opposed to 15.
Yup, but this is when doing char-by-char operations.
When using one or two memcpy() we have only two '%' intead of (perhaps) many 'if's.
Of course the memcpy() has its own while() loop but since it's optimized in assembly (and I guess we're not going to implement kfifo_get/put in assembly) I will stay with the memcpy + '%' version.
Stelian. -- Stelian Pop <stelian@popies.net> - 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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