Fix e_logl (128ibm) spurious underflow

[Andreas Jaeger]

On 03/27/2013 01:44 PM, Adhemerval Zanella wrote:
> Ping.
>
> On 03/14/2013 09:38 AM, Adhemerval Zanella wrote:
>> Ping.
>>
>> On 11-03-2013 09:27, Adhemerval Zanella wrote:
>>> Ping.
>>>
>>>
>>> On 03/07/2013 02:33 PM, Adhemerval Zanella wrote:
>>>> Ping.
>>>>
>>>> On 02/28/2013 02:02 AM, Adhemerval Zanella wrote:
>>>>> On 02/27/2013 08:50 PM, Joseph S. Myers wrote:
>>>>>> On Wed, 27 Feb 2013, Adhemerval Zanella wrote:
>>>>>>
>>>>>>> 2013-02-27  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
>>>>>>>
>>>>>>> 	* sysdeps/ieee754/ldbl-128ibm/e_logl.c (__ieee754_logl): Fix spurious
>>>>>>> 	underflow.
>>>>>>> 	* sysdeps/powerpc/fpu/libm-test-ulps: Update.
>>>>>> What is the bug report in Bugzilla for this issue, which presumably is
>>>>>> user-visible in a release so should have a bug report?  If there isn't
>>>>>> one, please file one; in any case, include the [BZ #N] annotation in the
>>>>>> ChangeLog entry (and a commit of a fix should include updating NEWS).
>>>>>> (If the issue isn't user-visible in a release and so doesn't need a bug
>>>>>> report, please explain why not.  But any bug being fixed that was
>>>>>> user-visible in a release should have a corresponding Bugzilla entry.)
>>>>>>
>>>>>> In my view you should add a testcase for this issue for log to
>>>>>> libm-test.inc, even if there are tests for other functions that show the
>>>>>> problem as well.
>>>>>>
>>>>> I create BZ #15214 to track this issue. I didn't add the specific testcase yet
>>>>> because it is showing some higher ULPs that I'd like to take a look (this is
>>>>> showing without my patch also).
>>>>>
>>>>> --
>>>>>
>>>>> 2013-02-28  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
>>>>>
>>>>> 	[BZ #15214]
>>>>> 	* NEWS: Mention BZ #15214.

Don't mention NEWS in the ChangeLog, just do it ;)

The rest looks fine to me,

Andreas

>>>>> 	* sysdeps/ieee754/ldbl-128ibm/e_logl.c (__ieee754_logl): Fix spurious
>>>>> 	underflow.
>>>>> 	* sysdeps/powerpc/fpu/libm-test-ulps: Update.
>>>>>
>>>>> diff --git a/NEWS b/NEWS
>>>>> index a4c5638..945aa9d 100644
>>>>> --- a/NEWS
>>>>> +++ b/NEWS
>>>>> @@ -11,7 +11,7 @@ Version 2.18
>>>>>
>>>>>     11561, 13951, 14142, 14200, 14317, 14327, 14496, 14920, 14964, 14981,
>>>>>     14982, 14985, 14994, 14996, 15003, 15006, 15020, 15023, 15036, 15054,
>>>>> -  15062, 15078, 15160.
>>>>> +  15062, 15078, 15160, 15214.
>>>>>
>>>>>   * Add support for calling C++11 thread_local object destructors on thread
>>>>>     and program exit.  This needs compiler support for offloading C++11
>>>>> diff --git a/sysdeps/ieee754/ldbl-128ibm/e_logl.c b/sysdeps/ieee754/ldbl-128ibm/e_logl.c
>>>>> index 14f47eb..15b5edf 100644
>>>>> --- a/sysdeps/ieee754/ldbl-128ibm/e_logl.c
>>>>> +++ b/sysdeps/ieee754/ldbl-128ibm/e_logl.c
>>>>> @@ -182,6 +182,9 @@ static const long double
>>>>>     ln2a = 6.93145751953125e-1L,
>>>>>     ln2b = 1.4286068203094172321214581765680755001344E-6L;
>>>>>
>>>>> +static const long double
>>>>> +  ldbl_epsilon = 0x1p-106L;
>>>>> +
>>>>>   long double
>>>>>   __ieee754_logl(long double x)
>>>>>   {
>>>>> @@ -258,7 +261,12 @@ __ieee754_logl(long double x)
>>>>>       }
>>>>>     /* Series expansion of log(1+z).  */
>>>>>     w = z * z;
>>>>> -  y = ((((((((((((l15 * z
>>>>> +  /* Avoid spurious underflows.  */
>>>>> +  if (__glibc_unlikely(w <= ldbl_epsilon))
>>>>> +    y = 0.0L;
>>>>> +  else
>>>>> +    {
>>>>> +      y = ((((((((((((l15 * z
>>>>>   		  + l14) * z
>>>>>   		 + l13) * z
>>>>>   		+ l12) * z
>>>>> @@ -271,7 +279,8 @@ __ieee754_logl(long double x)
>>>>>   	 + l5) * z
>>>>>   	+ l4) * z
>>>>>          + l3) * z * w;
>>>>> -  y -= 0.5 * w;
>>>>> +      y -= 0.5 * w;
>>>>> +    }
>>>>>     y += e * ln2b;  /* Base 2 exponent offset times ln(2).  */
>>>>>     y += z;
>>>>>     y += logtbl[k-26]; /* log(t) - (t-1) */
>>>>> diff --git a/sysdeps/powerpc/fpu/libm-test-ulps b/sysdeps/powerpc/fpu/libm-test-ulps
>>>>> index 4221967..5072190 100644
>>>>> --- a/sysdeps/powerpc/fpu/libm-test-ulps
>>>>> +++ b/sysdeps/powerpc/fpu/libm-test-ulps
>>>>> @@ -243,9 +243,11 @@ idouble: 1
>>>>>   Test "Real part of: cacos (-0.5 + +0 i) == 2.094395102393195492308428922186335256131 - 0 i":
>>>>>   double: 1
>>>>>   idouble: 1
>>>>> +ldouble: 1
>>>>>   Test "Real part of: cacos (-0.5 - 0 i) == 2.094395102393195492308428922186335256131 + +0 i":
>>>>>   double: 1
>>>>>   idouble: 1
>>>>> +ldouble: 1
>>>>>   Test "Imaginary part of: cacos (-1.5 + +0 i) == pi - 0.9624236501192068949955178268487368462704 i":
>>>>>   double: 1
>>>>>   float: 1
>>>>> @@ -265,6 +267,10 @@ double: 1
>>>>>   float: 1
>>>>>   idouble: 1
>>>>>   ifloat: 1
>>>>> +Test "Imaginary part of: cacos (0x1.fp1023 + 0x1.fp1023 i) == 7.853981633974483096156608458198757210493e-1 - 7.107906849659093345062145442726115449315e2 i":
>>>>> +ldouble: 1
>>>>> +Test "Imaginary part of: cacos (0x1.fp127 + 0x1.fp127 i) == 7.853981633974483096156608458198757210493e-1 - 8.973081118419833726837456344608533993585e1 i":
>>>>> +ldouble: 1
>>>>>
>>>>>   # cacosh
>>>>>   Test "Real part of: cacosh (+0 + 0.5 i) == 0.4812118250596034474977589134243684231352 + pi/2 i":
>


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  Andreas Jaeger aj@{suse.com,opensuse.org} Twitter/Identica: jaegerandi
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