linux-kernel - Re: [PATCH] utilities: add helper functions for safe 64-bit integer operations as 32-bit halves

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Message-Id: <20070421030825.bed0b8a9.akpm@linux-foundation.org>
Date:	Sat, 21 Apr 2007 03:08:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"John Anthony Kazos Jr." <jakj@...-k-j.com>
Cc:	James Bottomley <James.Bottomley@...elEye.com>,
	"Cameron, Steve" <Steve.Cameron@...com>,
	"Miller, Mike (OS Dev)" <Mike.Miller@...com>,
	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, trivial@...nel.org
Subject: Re: [PATCH] utilities: add helper functions for safe 64-bit integer
 operations as 32-bit halves

On Fri, 20 Apr 2007 20:55:49 -0400 (EDT) "John Anthony Kazos Jr." <jakj@...-k-j.com> wrote:

> +#define upper_32_bits(n) (sizeof(n) == 8 ? (u64)(n) >> 32 : 0)

It's very unclear what type this returns, in terms of both size and
signedness.  Perhaps it always returns a u64, dunno.  If it does, that will
cause the arithmetic which uses this macro to go 64-bit too.  Casting the
whole return value to u32 would fix all those doubts up.

> +#define lower_32_bits(n) (sizeof(n) == 8 ? (u32)(n) : (n))

n&0xffffffff would be simpler.

Do we actually have any call for this?
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