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SubjectRe: [PATCH] block: convert ata_port_for_each_link to use a while loop to reduce code size
Date
On Tue, 21 Oct 2008 21:24:32 +0100, "Richard Kennedy"
<richard@rsk.demon.co.uk> said:
> convert a for loop to a while loop in the ata_port_for_each_link macros
> to reduce code size.
>
> on x86_64 size reports reduction of text size in
> libata.ko : -272 bytes
> ahci.ko : -44 bytes
>
> Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
>
> ----
> This patch is against 2.6.27 git head.
>
> I've been running this patch on my AMD64 desktop machine for several
> days & have not seen any problems.
> regards
> Richard
>
>
> diff --git a/include/linux/libata.h b/include/linux/libata.h
> index 947cf84..bbe3b9d 100644
> --- a/include/linux/libata.h
> +++ b/include/linux/libata.h
> @@ -1283,12 +1283,12 @@ extern struct ata_link
> *__ata_port_next_link(struct ata_port *ap,
> bool dev_only);
>
> #define __ata_port_for_each_link(link, ap) \
> - for ((link) = __ata_port_next_link((ap), NULL, false); (link); \
> - (link) = __ata_port_next_link((ap), (link), false))
> + (link) = NULL; \
> + while (((link) = __ata_port_next_link((ap), (link), false)))

Hi Richard,

Please imagine how this expands...

if (some_condition)
__ata_port_for_each_link(link, ap)
do_something(...)

But it is probably possible to get the same size reduction by
changing the for-loop like this (safety parentheses left out):

for (link = NULL;
link = __ata_port_next_link(ap, link, false), link; )

Some programmers think this is abuse of the for-construct, though ;).

Greetings,
Alexander

> #define ata_port_for_each_link(link, ap) \
> - for ((link) = __ata_port_next_link((ap), NULL, true); (link); \
> - (link) = __ata_port_next_link((ap), (link), true))
> + (link) = NULL; \
> + while (((link) = __ata_port_next_link((ap), (link), true)))
>
> #define ata_link_for_each_dev(dev, link) \
> for ((dev) = (link)->device; \
--
Alexander van Heukelum
heukelum@fastmail.fm

--
http://www.fastmail.fm - mmm... Fastmail...



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