From: "H. Peter Anvin" <hpa@zytor.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: joerg.roedel@amd.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] introduce lower_32_bits() macro
Date: Fri, 25 Jul 2008 16:54:45 -0400 [thread overview]
Message-ID: <488A3D95.20108@zytor.com> (raw)
In-Reply-To: <20080725134759.ae19b883.akpm@linux-foundation.org>
Andrew Morton wrote:
>>> */
>>> #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.
>
> Yes, it will convert a 32-bit expression into a 64-bit one.
>
Sort of. upper_32_bits() takes a 32- or 64-bit expression, and delivers
the upper 32 bits *as a 32-bit number*. An equivalent expression would be:
((u32)((u64)(n) >> 32))
... which might actually produce better code, for all I know.
Logically speaking, if we have a lower_32_bits() macro, it should also
produce a 32-bit type as result.
-hpa
next prev parent reply other threads:[~2008-07-25 20:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-25 15:12 [PATCH] introduce lower_32_bits() macro Joerg Roedel
2008-07-25 16:06 ` H. Peter Anvin
2008-07-25 20:47 ` Andrew Morton
2008-07-25 20:54 ` Roland Dreier
2008-07-25 21:39 ` H. Peter Anvin
2008-07-25 20:54 ` H. Peter Anvin [this message]
2008-07-28 10:59 ` Joerg Roedel
2008-07-28 12:07 ` Joerg Roedel
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