Re: [Patch] xfs_lowbit64 broken on ia32

[Timothy Shimmin <tes@sgi.com>]

Alex Elder wrote:
> David Chinner wrote:
> . . .
>>>> Index: 2.6.x-xfs-new/fs/xfs/xfs_bit.h
>>>> ===================================================================
>>>> --- 2.6.x-xfs-new.orig/fs/xfs/xfs_bit.h	2007-11-02 
>>>> 13:44:45.000000000 +1100
>>>> +++ 2.6.x-xfs-new/fs/xfs/xfs_bit.h	2007-12-03 
>> 14:43:33.169851481 +1100
>>>> @@ -68,8 +68,8 @@ static inline int xfs_lowbit32(__uint32_
>>>> /* Get low bit set out of 64-bit argument, -1 if none set */
>>>> static inline int xfs_lowbit64(__uint64_t v)
>>>> {
>>>> -	unsigned long	t = v;
>>>> -	return (v) ? find_first_bit(&t, 64) : -1;
>>>> +	unsigned long long	t = v;
>>> Why create a local copy?  Why not just pass v into find_first_bit()?
>> Because I thought that taking the address of a function parameter
>> was a big no-no because the result is undefined (i.e. platform and
>> compiler dependent)?
> 
> I've never heard of this, and it's incorrect--at least with respect
> to standard C.  (But that's not to say in practice some compiler
> does it wrong.)  Unless it's a real (details known) problem you
> shouldn't try to work around it.
> 
> 					-Alex
> 
I've never heard of that either.
(Then again, I didn't know until recently that they changed C
  to allow "flexible array members" in C99
  http://tigcc.ticalc.org/doc/gnuexts.html#SEC75)

--Tim