[PATCH][BZ #16823] S390: Fix log1pl returning wrong infinity sign

[Stefan Liebler]

On 04/10/2014 12:09 AM, Ondřej Bílka wrote:
> On Wed, Apr 09, 2014 at 03:24:21PM +0200, Stefan Liebler wrote:
>> Hi,
>>
>> on S390 test-double fails for log1pl(-1) with infinity has wrong
>> sign in rounding mode FE_DOWNWARD. See Bug 16823.
>> In this rounding mode, (x-x) = -0.
>> In all other rounding modes, (x-x) = +0.
>> A division with divisor -0 leads to +inf, while +0 results in -inf
>> as expected. This patch changes the divisor to a const +0.
>> Tested on s390/s390x.
>>
>> Is this okay?
>>
> Looks ok.
>
> Perhaps we could add constants for infinity and nan would to write
> return value directly.
>
Thanks.

Returning a constant of infinity is not enough.
In this case an divide by zero exception should be raised, because 
log(0) is not defined.