On 06/15/15 11:09, Eric Blake wrote:
> On 06/15/2015 07:53 AM, Don Slutz wrote:
>> On 06/12/15 18:38, Eric Blake wrote:
>
>>>>
>>>> + /* Only support 1 address */
>>>> + if (addr) {
>>>> + return ~0U;
>>>> + }
>>>
>>> Different answer on 32-bit platforms (there, ~0U is 0xffffffff, which
>>> then 0-extends to uint64_t rather than your desired result of
>>> 0xffffffffffffffffULL).
>>>
>>
>> This is not true:
>
> Oh, I was confusing ~0UL (where sign extension on 32- vs 64-bit matters)
> and ~0U (which you used).
>
>>
>>> Why can't you just 'return -1;'?
>>>
>>
>> I/O instructions on x86 are limited to 32bits max. Also when EAX is
>> changed via inl, the high 32bits are 0. So the correct result is ~0U
>> not -1.
>
> Still, it might be better to write an explicit 0xffffffff or even have a
> named constant, rather than making people reason about whether ~0U
> promotes into a 64-bit value with only 32 bits set.
>
Ok, Will switch to 0xffffffff.
-Don Slutz
