linux-kernel - Re: [PATCH] Optimize int_sqrt for small values for faster idle

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Message-ID: <1454373398.7627.193.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 01 Feb 2016 16:36:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andi Kleen <ak@...ux.intel.com>, Andi Kleen <andi@...stfloor.org>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	davidlohr.bueso@...com, rafael.j.wysocki@...el.com, lenb@...nel.org
Subject: Re: [PATCH] Optimize int_sqrt for small values for faster idle

On Tue, 2016-02-02 at 00:08 +0100, Rasmus Villemoes wrote:

> Thanks. (Is there a good way to tell gcc that avg*avg is actually a
> 32x32->64 multiplication?)

If avg is 32bit, compiler does that for you.

u32 avg = ...

u64 result = (u64)avg * avg;