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Date: Fri, 21 Dec 2018 13:07:21 -0800
From: Matthew Wilcox <>
To: Cyrill Gorcunov <>
Cc: Igor Stoppa <>,
	Andy Lutomirski <>,
	Peter Zijlstra <>,
	Dave Hansen <>,
	Mimi Zohar <>,
	Thiago Jung Bauermann <>,, Nadav Amit <>,
	Kees Cook <>,
	Ahmed Soliman <>,,,,
Subject: Re: [PATCH 01/12] x86_64: memset_user()

On Fri, Dec 21, 2018 at 11:46:16PM +0300, Cyrill Gorcunov wrote:
> Cast to unsigned char is needed in any case. And as far as I remember
> we've been using this multiplication trick for a really long time
> in x86 land. I'm out of sources right now but it should be somewhere
> in assembly libs.

x86 isn't the only CPU.  Some CPUs have slow multiplies but fast shifts.
Also loading 0x0101010101010101 into a register may be inefficient on
some CPUs.

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