linux-kernel - Re: [PATCH] introduce lower_32

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Date:	Fri, 25 Jul 2008 12:06:27 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] introduce lower_32_bits() macro

Joerg Roedel wrote:
> The file kernel.h contains the upper_32_bits macro. This patch adds the other
> part, the lower_32_bits macro. Its first use will be in the driver for AMD
> IOMMU.
> 
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  include/linux/kernel.h |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index f9cd7a5..6fd2977 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -73,6 +73,12 @@ extern const char linux_proc_banner[];
>   */
>  #define upper_32_bits(n) ((u32)(((n) >> 16) >> 16))
>  
> +/**
> + * lower_32_bits - return bits 0-31 of a number
> + * @n: the number we're accessing
> + */
> +#define lower_32_bits(n) ((n) & 0xffffffffULL)
> +

NAK.  These are assymmetric with regards to type, which is the *last* 
thing we want.

The symmetric definition would be ((u32)(n)), but that's already 
idiomatic use, so why not use it as-is?

	-hpa

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