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From: <cutaway@bellsouth.net>
To: <7eggert@gmx.de>, "Gene Heskett" <gene.heskett@verizon.net>,
	<linux-kernel@vger.kernel.org>
Subject: Re: .../asm-i386/bitops.h  performance improvements
Date: Wed, 15 Jun 2005 19:53:27 -0400	[thread overview]
Message-ID: <000201c57207$72016a00$2800000a@pc365dualp2> (raw)
In-Reply-To: E1DiZKe-0000em-58@be1.7eggert.dyndns.org

Ummm, in simple terms - this statement is flat out 100% wrong.

LEA with the SIB byte has been around since 386 and is included on every CPU
Linux is capable of running on.

Compile this using -m386 and look at the ASM listing file and convince
yourself.

unsigned int foo(int bar)
{
return ((bar<<3)+bar);
}

GCC is going to generate a MOV of parm to EAX, then a LEA EAX,[EAX+EAX*8]

Don't trust me - compile this and prove it to yourself.


----- Original Message ----- 
From: "Bodo Eggert" <harvested.in.lkml@posting.7eggert.dyndns.org>
To: "Gene Heskett" <gene.heskett@verizon.net>; <cutaway@bellsouth.net>;
<linux->
>
> However, the multiplicator is not documented for i486, therefore it will
be a i586
> extension.


  parent reply	other threads:[~2005-06-15 23:18 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <4fB8l-73q-9@gated-at.bofh.it>
     [not found] ` <4fF2j-1Lo-19@gated-at.bofh.it>
2005-06-15 14:57   ` .../asm-i386/bitops.h performance improvements Bodo Eggert
2005-06-15 15:30     ` Maciej W. Rozycki
2005-06-15 16:06       ` Richard B. Johnson
2005-06-15 16:29         ` Maciej W. Rozycki
2005-06-15 19:10           ` Bodo Eggert
2005-06-16  3:26             ` Stephen Rothwell
2005-06-16  7:10             ` Mikael Pettersson
2005-06-15 23:53     ` cutaway [this message]
2005-06-15  8:53 cutaway
2005-06-15 12:18 ` Gene Heskett
2005-06-15 13:06   ` Richard B. Johnson
2005-06-15 19:18   ` cutaway
2005-06-15 15:34 ` Maciej W. Rozycki
2005-06-15 23:48   ` cutaway

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