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

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

Hi,

log1pl (-1) now returns with -inf instead of +inf in FE_DOWNWARD 
rounding mode. The source code producing the -inf for the double/float 
variants is the same, but on S390 the compiler generates a division by 
constant +zero and ignores the (x-x).
Thus i also changed it to the constant zero in the double/float functions.
IÂve tested it on S390.
Please test it on other platforms because there are also reports for the 
same failure on aarch64 (see bug comment 1)
and sparc (https://www.sourceware.org/ml/libc-alpha/2014-04/msg00410.html).

Give feedback in order to commit the patch.

Bye

---
2014-04-22  Stefan Liebler  <stli@linux.vnet.ibm.com>

	[BZ #16823]
	* sysdeps/ieee754/ldbl-128/s_log1pl.c (__log1pl):
	Always divide by positive zero when computing -Inf result.
	* sysdeps/ieee754/dbl-64/s_log1p.c (__log1p): Likewise.
	* sysdeps/ieee754/flt-32/s_log1pf.c (__log1pf): Likewise.
---

On 04/09/2014 03:24 PM, 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?
>
> Bye
>
> ---
> 2014-04-09  Stefan Liebler  <stli@linux.vnet.ibm.com>
>
>      [BZ #16823]
>      * sysdeps/ieee754/ldbl-128/s_log1pl.c (__log1pl):
>      Use const positive zero instead of (x-x).
> ---

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