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List:       linux-kernel
Subject:    Re: [PATCH 2/9] drivers/acpi/asus_acpi.c: Correct use of ! and &
From:       Andrew Morton <akpm () linux-foundation ! org>
Date:       2008-02-29 21:33:20
Message-ID: 20080229133320.1ec95e84.akpm () linux-foundation ! org
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On Fri, 29 Feb 2008 19:06:48 +0100
Mark Pearson <devnull.port@googlemail.com> wrote:

> Andrew Morton wrote:
> >> Seems an odd way of doing:
> >>
> >> 	led_out ^= 0x01;
> > 
> > It does.
> > 
> >> It this due to some optimisation?
> > 
> > Surely not ;)
> >
> ;) Thought so - one doesn't like to be too presumptuous ;)
> 
> > That code has been there for many years.
> > 
> > I changed the patch to this:
> > 
> > --- a/drivers/acpi/asus_acpi.c~drivers-acpi-asus_acpic-correct-use-of-and
> > +++ a/drivers/acpi/asus_acpi.c
> > @@ -610,7 +610,7 @@ write_led(const char __user * buffer, un
> >  	    (led_out) ? (hotk->status | ledmask) : (hotk->status & ~ledmask);
> >  
> >  	if (invert)		/* invert target value */
> > -		led_out = !led_out & 0x1;
> > +		led_out = !led_out;
> >  
> >  	if (!write_acpi_int(hotk->handle, ledname, led_out, NULL))
> >  		printk(KERN_WARNING "Asus ACPI: LED (%s) write failed\n",
> > _
> > 
> > 
> 
> Is the ! operator architecture/compiler dependent?

It shouldn't be.

> or can one always say that
> !NON_ZERO_VALUE == 0 and !0 == 1?
> 

I always have ;)  I expect it's in the C standard somewhere.
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