Re: [PATCH 2/9] drivers/acpi/asus_acpi.c: Correct use of ! and &

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 27 Feb 2008 19:29:15 +0100 Mark Pearson <devnull.port@googlemail.com> wrote:

> Karol Kozimor wrote:
> > On 26-02-2008, at 21:42, Julia Lawall wrote:
> >>      if (invert)        /* invert target value */
> >> -        led_out = !led_out & 0x1;
> >> +        led_out = !(led_out & 0x1);
> >>
> >>      if (!write_acpi_int(hotk->handle, ledname, led_out, NULL))
> >>          printk(KERN_WARNING "Asus ACPI: LED (%s) write failed\n",
> > 
> > 
> > IIRC we're just supposed to flip the last bit here, so the original code
> > is correct.
> > Best regards,
> > 
> 
> Seems an odd way of doing:
> 
> 	led_out ^= 0x01;

It does.

> It this due to some optimisation?

Surely not ;)

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",
_