Fix ldbl-128ibm log1pl (-1) sign of infinity (bug 19076).

The ldbl-128ibm implementation of log1pl produces an infinity with the
wrong sign for log1pl (-1) in FE_DOWNWARD mode.  This patch fixes this
by changing a division (-1.0L / (x - x)) (incorrect in FE_DOWNWARD
mode) to (-1.0L / 0.0L) (correct in all rounding modes).

Tested for powerpc.

	[BZ #19076]
	* sysdeps/ieee754/ldbl-128ibm/s_log1pl.c (__log1pl): Divide by
	constant 0.0L when computing infinite result.

3 files changed, 8 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 6cb9b73dc6..17388a7927 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2015-10-06  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #19076]
+	* sysdeps/ieee754/ldbl-128ibm/s_log1pl.c (__log1pl): Divide by
+	constant 0.0L when computing infinite result.
+
 2015-10-06  Florian Weimer  <fweimer@redhat.com>
 
 	[BZ #10432]
diff --git a/NEWS b/NEWS
index 3852e7f3e1..b93a5dc4e9 100644
--- a/NEWS
+++ b/NEWS
@@ -18,7 +18,7 @@ Version 2.23
   18820, 18823, 18824, 18825, 18857, 18863, 18870, 18872, 18873, 18875,
   18887, 18921, 18951, 18952, 18956, 18961, 18966, 18967, 18969, 18970,
   18977, 18980, 18981, 18985, 19003, 19012, 19016, 19018, 19032, 19046,
-  19049, 19050, 19059, 19071.
+  19049, 19050, 19059, 19071, 19076.
 
 * The obsolete header <regexp.h> has been removed.  Programs that require
   this header must be updated to use <regex.h> instead.
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_log1pl.c b/sysdeps/ieee754/ldbl-128ibm/s_log1pl.c
index a0e24d7f22..ad9a1fe20f 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_log1pl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_log1pl.c
@@ -149,7 +149,7 @@ __log1pl (long double xm1)
   if (x <= 0.0L)
     {
       if (x == 0.0L)
-	return (-1.0L / (x - x));
+	return (-1.0L / 0.0L);
       else
 	return (zero / (x - x));
     }