Messages in this thread | | | Date | Fri, 29 Feb 2008 12:01:26 +0100 (CET) | From | Julia Lawall <> | Subject | Re: [PATCH 2/9] drivers/acpi/asus_acpi.c: Correct use of ! and & |
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On Thu, 28 Feb 2008, Andrew Morton wrote:
> 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;
I don't think this is the same:
!(0110 & 0x01) = !0 = 1 !0110 = 0
led_out ^= 0x01;
is also not the same:
0110 ^ 0x01 = 0111
Is it desired to keep the value and flip the last bit or just obtain the opposite of the last bit?
julia
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