From: Michal Nazarewicz <mina86@tlen.pl>
To: Tim Walberg <twalberg@comcast.net>
Cc: ratheesh k <ratheesh.ksz@gmail.com>, linux-c-programming@vger.kernel.org
Subject: Re: union to get parts of integer
Date: Mon, 20 Dec 2010 16:40:14 +0100 [thread overview]
Message-ID: <8762uotpup.fsf@erwin.mina86.com> (raw)
In-Reply-To: <20101220153008.GH16355@comcast.net> (Tim Walberg's message of "Mon, 20 Dec 2010 09:30:08 -0600")
Tim Walberg <twalberg@comcast.net> writes:
> It's likely that either the union or direct pointer expressions yield
> more efficient code, as they can probably be compiled to direct byte-width
> load/store instructions, rather than shifts and logical ands... However,
> if the code's not in a critical path for performance, it probably won't
> matter. And on some architectures, there may not be byte-width operations,
> I guess...
It's not the issue of performance. It's an issue of whether you want
each separate byte as saved in memory (which should rarely be the case)
or if you want specific part of the value.
> On 12/20/2010 15:44 +0100, Michal Nazarewicz wrote:
>>>
>>> ((char *)&i)[0].
>>>
>>> However, are you sure that you need this? Don't you need "(i & 255)",
>>> "((i >> 8) & 255)", etc. instead?
>>>
>>> --
>>> Best regards, _ _
>>> .o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
>>> ..o | Computer Science, Michal "mina86" Nazarewicz (o o)
>>> ooo +--<mina86-tlen.pl>--<jid:mina86-jabber.org>--ooO--(_)--Ooo--
--
Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
ooo +--<mina86-tlen.pl>--<jid:mina86-jabber.org>--ooO--(_)--Ooo--
next prev parent reply other threads:[~2010-12-20 15:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-20 10:40 union to get parts of integer ratheesh k
2010-12-20 12:03 ` Reza Hoorfar
2010-12-20 14:44 ` Michal Nazarewicz
2010-12-20 15:30 ` Tim Walberg
2010-12-20 15:40 ` Michal Nazarewicz [this message]
2010-12-21 16:22 ` Glynn Clements
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