[PATCH 07/14] Cleanup: avoid undefined shift operation

[Dirk Hohndel]

> On Jan 3, 2018, at 7:23 AM, Jef Driesen <jef at libdivecomputer.org> wrote:
> 
> On 29-12-17 08:00, Linus Torvalds wrote:
>> On Thu, Dec 28, 2017 at 4:35 PM, Dirk Hohndel <dirk at hohndel.org> wrote:
>>>         unsigned int signbit = (1 << (n - 1));
>>> -       unsigned int mask = (0xFFFFFFFF << n);
>>> +       unsigned int mask;
>>> +
>>> +       // shifting a 32bit constant by more than 31 bits has undefined behavior
>>> +       if (n == 32)
>>> +               mask = 0;
>>> +       else
>>> +               mask = (0xFFFFFFFF << n);
>> Ugh. That's ugly.
>> It's much simpler to just do
>>         unsigned int mask = ~(signbit-1);
>> instead.
>> Yes, that mask ends up including the sign bit (the old mask did not),
>> but that doesn't matter for the end result.
> 
> That's indeed an easier and nicer fix!
> 
> The bitwise not can even be omitted from the mask, and moved to the return statements (where there is already both a mask and a ~mask).

I will update accordingly.

/D