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Re: Fix e_logl (128ibm) spurious underflow

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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