Re: [PATCH 2/3] Simplify wrapped binops

["Bin.Cheng" <amker dot cheng at gmail dot com>]

On Fri, May 19, 2017 at 11:09 AM, Robin Dapp <rdapp@linux.vnet.ibm.com> wrote:
>> I can guess what is happening here.  It's a 40 bits unsigned long long
>> field, (s.b-8) will be like:
>> _1 = s.b
>> _2 = _1 + 0xfffffffff8
>> Also get_range_info returns value range [0, 0xFFFFFFFFFF] for _1.
>> You'd need to check if _1(with range [0, 0xFFFFFFFFFF]) + 0xfffffffff8
>> overflows against precision of the bit-field which is 40 bits
>> precision.  The failure might because overflowness is checked against
>> unsigned long long's precision which is 64 bits.
>
>>> Also, is there a possibility to know if there was an "ok" overflow or
>>> not from get_range_info ()'s output? Would I have to compare the result
>>> with the involved variable's range?
>> I think you have to check it manually against max/min value of that
>> type precision.
>
> Currently, extract_... () does that all that for me, is it really too
> expensive to call? I guess, using get_range_info first and calling
> extract when get_range_info returns a VR_RANGE is not really a favorable
> thing to do either? :)
Not only the cost, we should avoid introducing more interfaces while
old ones can do the work.  Anyway, it's Richard's call here.

Thanks,
bin
>
> Regards
>  Robin
>