[PATCH 05/18] Fix 64bit arch issue in synaptics eventcomm.c

[Henrik Rydberg]

On 10/08/2010 10:51 PM, Mark Kettenis wrote:

>> Date: Fri, 08 Oct 2010 21:36:02 +0200
>> From: Takashi Iwai <tiwai at suse.de>
>>
>> At Fri, 8 Oct 2010 20:48:10 +0200 (CEST),
>> Mark Kettenis wrote:
>>>
>>>> From: Takashi Iwai <tiwai at suse.de>
>>>> Date: Fri,  8 Oct 2010 19:22:29 +0200
>>>
>>> Sorry, but it isn't obvious to me what issue this fixes.
>>
>> In C, "1" is an integer, not an unsigned long.
>> Thus (1 << 33) doesn't give you the 33th bit shift, but it's undefined.
> 
> But if you'd actually use 33 (or event 32) as an offset, things
> wouldn't work on a 32-bit platform would they?


I believe this is what the patch is supposed to fix.


> Anyway,
> 
>> If any, this must be (1UL << 32). 
> 
> This is the idiom that is much more common.  I probably wouldn't have
> questioned things if you'd written it like that.  I recommend you to
> stick to this version.


For a counter-example, see the definition of test_bit() in the Linux kernel.

>> Also, it'd be better if such a test macro returns 1 instead of a
>> random non-zero value.  So does my patch.
> 
> In C this doesn't matter.


It is still useful to know if a logic expression evaluates to (0, 1) or (0,
nonzero).

Henrik