Fix ldbl-128 / ldbl-128ibm lgammal spurious underflow (bug 16400).

This patch fixes bug 16400, spurious underflow exceptions for ldbl-128
/ ldbl-128ibm lgammal with small positive arguments, by just using
-__logl (x) as the result in the problem cases (similar to the
previous fix for problems with small negative arguments).

Tested powerpc32, and also tested on mips64 that this does not require
ulps regeneration for the ldbl-128 case.

	* sysdeps/ieee754/ldbl-128/e_lgammal_r.c (__ieee754_lgammal_r):
	Return -__logl (x) for small positive arguments without evaluating
	a polynomial.

diff --git a/ChangeLog b/ChangeLog
index 1984691..8bdea17 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2014-01-06  Joseph Myers  <joseph@codesourcery.com>
+
+       [BZ #16400]
+       * sysdeps/ieee754/ldbl-128/e_lgammal_r.c (__ieee754_lgammal_r):
+       Return -__logl (x) for small positive arguments without evaluating
+       a polynomial.
+
 2014-01-06  Mike Frysinger  <vapier@gentoo.org>
 
        * sysdeps/unix/sysv/linux/sys/ptrace.h (ptrace_peeksiginfo_args):

diff --git a/NEWS b/NEWS
index e6c5020..ab3b882 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -24,7 +24,7 @@ Version 2.19
   16112, 16143, 16144, 16146, 16150, 16151, 16153, 16167, 16172, 16195,
   16214, 16245, 16271, 16274, 16283, 16289, 16293, 16314, 16316, 16330,
   16337, 16338, 16356, 16365, 16366, 16369, 16372, 16375, 16379, 16384,
-  16385, 16386, 16390.
+  16385, 16386, 16390, 16400.
 
 * Slovenian translations for glibc messages have been contributed by the
   Translation Project's Slovenian team of translators.

diff --git a/sysdeps/ieee754/ldbl-128/e_lgammal_r.c b/sysdeps/ieee754/ldbl-128/e_lgammal_r.c
index 23ab9b9..1961355 100644 (file)
--- a/sysdeps/ieee754/ldbl-128/e_lgammal_r.c
+++ b/sysdeps/ieee754/ldbl-128/e_lgammal_r.c
@@ -805,7 +805,9 @@ __ieee754_lgammal_r (long double x, int *signgamp)
        {
        case 0:
          /* log gamma (x + 1) = log(x) + log gamma(x) */
-         if (x <= 0.125)
+         if (x < 0x1p-120L)
+           return -__logl (x);
+         else if (x <= 0.125)
            {
              p = x * neval (x, RN1, NRN1) / deval (x, RD1, NRD1);
            }