linux-kernel - Re: [PATCH] treewide: Add and use ADD

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Date:	Mon, 29 Mar 2010 12:47:08 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Jiri Kosina <trivial@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] treewide: Add and use ADD_MOD macro

On Sun, 28 Mar 2010 14:57:27 -0700 Joe Perches wrote:

> Add a macro for the somewhat common use of
> 
> 	(something + value) % value
> 
> drivers/net/sundance.c includes a change from
> a for(;test;add) loop to while (test) {... add};
> because the test uses ADD_MOD
> 
> Compile tested only
> 
> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
>  include/linux/kernel.h                  |    1 +
>  drivers/ata/libata-eh.c                 |    2 +-
>  drivers/media/video/ov511.c             |    2 +-
>  drivers/media/video/usbvideo/usbvideo.c |    2 +-
>  drivers/net/dl2k.c                      |    8 ++++----
>  drivers/net/sundance.c                  |    4 ++--
>  drivers/pci/dmar.c                      |    6 +++---
>  drivers/scsi/3w-9xxx.c                  |    2 +-
>  drivers/staging/wavelan/wavelan_cs.c    |   10 +++++-----
>  drivers/usb/misc/sisusbvga/sisusb_con.c |    4 ++--
>  drivers/video/console/vgacon.c          |    4 ++--
>  sound/oss/vwsnd.c                       |    6 +++---
>  12 files changed, 26 insertions(+), 25 deletions(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 7f07074..c96b1ac 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -63,6 +63,7 @@ extern const char linux_proc_banner[];
>  	(((x) + ((__divisor) / 2)) / (__divisor));	\
>  }							\
>  )
> +#define ADD_MOD(x, y) (((x) + (y)) % (y))
>  
>  #define _RET_IP_		(unsigned long)__builtin_return_address(0)
>  #define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })


It would be better not to evaluate y more than one time.

Also it's not safe for 64-bit 'y' on i386, right?
Looks like it would cause missing reference to __imoddi3 or whatever it is called.

so it can easily be misused IMO.

---
~Randy
--
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