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Subject: Re: RFC: booleans and the kernel
From: Robert Love <rml@tech9.net>
To: root@chaos.analogic.com
Cc: Oliver Xymoron <oxymoron@waste.org>,
        Jeff Garzik <jgarzik@mandrakesoft.com>,
        Linux-Kernel list <linux-kernel@vger.kernel.org>
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Date: 24 Jan 2002 17:13:05 -0500
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On Thu, 2002-01-24 at 16:55, Richard B. Johnson wrote:

> Don't you wish!
> [snip]
> 	cmpl $0,8(%ebp)      <-------------- Compare against zero.

Ah, but you compiled without optimization.  Using your example program,
`gcc -Wall -S example.c' gives me the same output as you.  But with -O2
I get:

foo:
	pushl	%ebp
	movl	%esp, %ebp
	movl	8(%ebp), %edx
	xorl	%eax, %eax
	testl	%edx, %edx
	sete	%al
	popl	%ebp
	ret

Which is the XOR and self-test with no constant Oliver described.

	Robert Love

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