Fix e_logl (128ibm) spurious underflow

diff --git a/ChangeLog b/ChangeLog
index 7c1543c..390c5cb 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2013-03-28  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
+
+       [BZ #15214]
+       * sysdeps/ieee754/ldbl-128ibm/e_logl.c (__ieee754_logl): Fix spurious
+       underflow.
+       * sysdeps/powerpc/fpu/libm-test-ulps: Update.
+
 2013-03-28  Siddhesh Poyarekar  <siddhesh@redhat.com>
 
        [BZ #15304]

diff --git a/NEWS b/NEWS
index 0902478..0682b19 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -11,8 +11,8 @@ Version 2.18
 
   11120, 11561, 12723, 13550, 13889, 13951, 14142, 14176, 14200, 14317,
   14327, 14496, 14812, 14920, 14964, 14981, 14982, 14985, 14994, 14996,
-  15003, 15006, 15020, 15023, 15036, 15054, 15055, 15062, 15078, 15160,
-  15232, 15234, 15283, 15285, 15287, 15304, 15307.
+  15003, 15006, 15020, 15023, 15036, 15054, 15055, 15062, 15078, 15124,
+  15160, 15232, 15234, 15283, 15285, 15287, 15304, 15307.
 
 * 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 (file)
--- 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 (file)
--- 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":