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Date: Sat, 21 Apr 2007 03:08:25 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "John Anthony Kazos Jr." <jakj@j-a-k-j.com>
Cc: James Bottomley <James.Bottomley@SteelEye.com>,
       "Cameron, Steve" <Steve.Cameron@hp.com>,
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       linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org,
       trivial@kernel.org
Subject: Re: [PATCH] utilities: add helper functions for safe 64-bit integer
 operations as 32-bit halves
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On Fri, 20 Apr 2007 20:55:49 -0400 (EDT) "John Anthony Kazos Jr." <jakj@j-a-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?