linux-kernel - Re: [tip:x86/asm] x86, bitops: Change bitops to be native operand size

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Date:	Mon, 11 Nov 2013 15:34:39 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Joe Perches <joe@...ches.com>, "H. Peter Anvin" <hpa@...or.com>
CC:	linux-arch <linux-arch@...r.kernel.org>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	james.t.kukunas@...el.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [tip:x86/asm] x86, bitops:  Change bitops to be native operand
 size

On 11/10/2013 06:22 PM, Joe Perches wrote:
> 
> Perhaps the current x86 bitops asm code is being conflated
> with the ideal implementation?
> 

Yes, by you.

x86 has instructions that operate on signed bitindicies.  It doesn't
have instructions that operate on unsigned bitindicies.  Unless someone
is willing to do the work to prove that shift and mask is actually
faster than using the hardware instructions (which I doubt, but it is
always a possibility), that's what we have.

	-hpa

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