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From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <dada1@cosmosbay.com>,
	Davide Libenzi <davidel@xmailserver.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch v2] epoll use a single inode ...
Date: Tue, 06 Mar 2007 21:40:13 -0800	[thread overview]
Message-ID: <45EE503D.10608@zytor.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0703061944590.5963@woody.linux-foundation.org>

Linus Torvalds wrote:
> 
> On Tue, 6 Mar 2007, Eric Dumazet wrote:
>> I did a user space program, attached to this mail.
>>
>> I rewrote the reciprocal_div() for i386 so that one multiply is used.
> 
> Ok, this is definitely faster on Core 2 as well, so "numbers talk, 
> bullshit walks". No more objections.
> 
> (That said, I bet you could do even better for octal and hex numbers, so 
> if you *really* want to speed things up, you should just make a 
> special-case routine for each base (there's just three of them), and you 
> can then also optimize the base-10 thing much better (you can do two 
> digits at a time by dividing by 100, etc)
> 

Of course you can do better for octal and hex -- it's just shift and mask.

Decimal is trickier; however, at least on i386 it might make sense to 
divide by 100 and then use the AAM instruction, or a table lookup, to 
split it into individual digits.

	-hpa

  reply	other threads:[~2007-03-07  5:40 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-03-05 23:41 [patch v2] epoll use a single inode Davide Libenzi
2007-03-06  0:00 ` Linus Torvalds
2007-03-06  0:12   ` Davide Libenzi
2007-03-06  0:20     ` Davide Libenzi
2007-03-06  0:25     ` Linus Torvalds
2007-03-06  2:25       ` H. Peter Anvin
2007-03-06  2:34         ` Davide Libenzi
2007-03-06  2:37           ` H. Peter Anvin
2007-03-06  2:43             ` Davide Libenzi
2007-03-06  6:22               ` Eric Dumazet
2007-03-06  6:31                 ` Davide Libenzi
2007-03-06  6:37                   ` Davide Libenzi
2007-03-06 16:28                 ` H. Peter Anvin
2007-03-06 17:09                   ` Linus Torvalds
2007-03-06 17:14                     ` H. Peter Anvin
2007-03-06 17:12                   ` Eric Dumazet
2007-03-06 17:19                     ` Linus Torvalds
2007-03-06 17:27                       ` H. Peter Anvin
2007-03-06 17:28                       ` Eric Dumazet
2007-03-06 18:10                         ` Eric Dumazet
2007-03-06 20:20                           ` Eric Dumazet
2007-03-07  3:47                             ` Linus Torvalds
2007-03-07  5:40                               ` H. Peter Anvin [this message]
2007-03-07  6:57                               ` Eric Dumazet
2007-03-07  7:13                                 ` H. Peter Anvin
2007-03-07 23:46                             ` Sami Farin
2007-03-06 18:10                   ` Davide Libenzi
2007-03-10  8:06     ` Pavel Machek
2007-03-10  8:24       ` Davide Libenzi

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