Use of C99 extra long double math functions after r236148

[Stephen Montgomery-Smith]

On 07/20/2012 09:33 PM, Bruce Evans wrote:
> On Fri, 20 Jul 2012, Stephen Montgomery-Smith wrote:
>
>> On 07/20/2012 11:25 AM, Bruce Evans wrote:
>>> On Fri, 20 Jul 2012, Stephen Montgomery-Smith wrote:
>>
>>
>>> %             x0 = (float)x;
>>> %             x1 = x - x0;
>>> %             y0 = (float)y;
>>> %             y1 = y - y0;
>>>
>>> A good way to do the hi+lo decompositions.
>>
>> That was the way I tried first.  But it didn't work for me!
>>
>> But I see you changed things further down, so that is probably why it
>> works for you.
>
> I didn't understand what was happening before, but think I can explain it
> now:
> - the above gives correct hi+lo decompositions.  Both hi and lo are usually
>    nonzero.  The code below did't really understand hi+lo decompositions,
>    and often increases the final error (relative to naive code).
> - your code often gives null but backwards hi+lo decompositions, with hi
> = 0
>    and lo = full value.  The code below did't really understand hi+lo
>    decompositions.  But when hi = 0, it is especially easy to add and
>    multiply it exactly, so the final error isn't increased so often.

Yes.  That was my intention.  But I will go with whatever works best - I 
am not sold on one solution over another.