From: Richard Henderson <rth@twiddle.net>
To: Markus Armbruster <armbru@redhat.com>,
Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2] utils: Add pow2ceil()
Date: Thu, 12 Mar 2015 08:29:16 -0700 [thread overview]
Message-ID: <5501B0CC.3090500@twiddle.net> (raw)
In-Reply-To: <877fv6gth5.fsf@blackfin.pond.sub.org>
On 02/25/2015 02:45 AM, Markus Armbruster wrote:
> return 0x8000000000000000u >> (clz64(value - 1) - 1);
I realize this was weeks ago, but it would certainly be preferable to shift a
small constant left than a large constant right.
Most RISC machines can't form 0x8000000000000000ull without loading 1 and then
left shifting to start with. So end the end you're better off with
return 1ull << (63 - clz64(value));
r~
next prev parent reply other threads:[~2015-03-12 15:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-23 12:23 [Qemu-devel] [PATCH v2] utils: Add pow2ceil() Alexey Kardashevskiy
2015-02-23 13:59 ` Markus Armbruster
2015-02-23 16:17 ` Eric Blake
2015-02-23 17:40 ` Markus Armbruster
2015-02-23 21:20 ` Eric Blake
2015-02-24 9:39 ` Markus Armbruster
2015-02-24 11:39 ` Peter Maydell
2015-02-24 13:09 ` Markus Armbruster
2015-02-25 0:40 ` Alexey Kardashevskiy
2015-02-25 10:45 ` Markus Armbruster
2015-03-12 15:29 ` Richard Henderson [this message]
2015-03-12 16:45 ` Eric Blake
2015-03-13 19:04 ` Richard Henderson
2015-03-13 7:33 ` Markus Armbruster
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