From: "George Spelvin" <linux@horizon.com>
To: peterz@infradead.org, zhaoxiu.zeng@gmail.com
Cc: akpm@linux-foundation.org, dhowells@redhat.com,
jwboyer@redhat.com, linux-kernel@vger.kernel.org,
linux@horizon.com, mingo@kernel.org, takahiro.akashi@linaro.org
Subject: Re: [PATCH 1/1] GCD: add binary GCD algorithm
Date: 15 Aug 2014 16:16:01 -0400 [thread overview]
Message-ID: <20140815201601.2497.qmail@ns.horizon.com> (raw)
In-Reply-To: <20140815135855.GG19379@twins.programming.kicks-ass.net>
> So I looked at wikipedia (I wasn't aware of this algorithm, clever
> though), and am still somewhat puzzled by your 'r'.
>
> What's 'wrong' with their iterative version, or what's better about your
> 'r' stuff?
I need to look more carefully, but it looks nifty.
Basically, it's avoiding the usual issue of counting the lsbits to factor
out a power of 2.
Rather than taking out the common factors of 2 a bit at a time, to
reduce to the case where one is even and one is odd (i.e. ((a ^ b) & 1)
== 1), just find the low-order differing bit and use that instead of
"1" in the algorithm. I.e. ((1 ^ b) & r) == r.
I have to see if there's a nicer way to arrange things, but it looks good.
What I'd like is a better way to automatically configure "divide is
slow" from an architecture.
next prev parent reply other threads:[~2014-08-15 20:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-15 12:49 [PATCH 1/1] GCD: add binary GCD algorithm Zhaoxiu Zeng
2014-08-15 13:58 ` Peter Zijlstra
2014-08-15 16:41 ` zhaoxiu.zeng
2014-08-15 21:53 ` George Spelvin
2014-08-15 20:16 ` George Spelvin [this message]
2014-08-15 21:32 ` Peter Zijlstra
2014-08-22 21:31 ` Andrew Morton
2014-08-22 22:36 ` George Spelvin
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