From 4c327f2ad89cff8e1fb6f7fe09b398119783553a Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 8 Jan 2014 13:32:39 +0000 Subject: [PATCH] Fix ldbl-128ibm expm1l on large arguments (bug 16408). This patch fixes bug 16408, ldbl-128ibm expm1l returning NaN for some large arguments. The basic problem is that the approach of converting the exponent to the form n * log(2) + y, where -0.5 <= y <= 0.5, then computing 2^n * expm1(y) + (2^n - 1) falls over when 2^n overflows (starting slightly before the point where expm1 overflows, when y is negative and n is the least integer for which 2^n overflows). The ldbl-128 code, and the x86/x86_64 code, make expm1l fall back to expl for large positive arguments to avoid this issue. This patch makes the ldbl-128ibm code do the same. (The problem appears for the particular argument in the testsuite because the ldbl-128ibm code also uses an overflow threshold that's for ldbl-128 and is too big for ldbl-128ibm, but the problem described applies for large non-overflowing cases as well, although during the freeze is not a suitable time for making the expm1 tests cover cases close to overflow more thoroughly.) This leaves some code for large positive arguments in expm1l that is now dead. To keep the code for ldbl-128 and ldbl-128ibm similar, and to avoid unnecessary changes during the freeze, the patch doesn't remove it; instead I propose to file a bug in Bugzilla as a reminder that this code (for overflow, including errno setting, and for arguments of +Inf) is no longer needed and should be removed from both those expm1l implementations. Tested powerpc32. * sysdeps/ieee754/ldbl-128ibm/s_expm1l.c (__expm1l): Use __expl for large positive arguments. --- ChangeLog | 6 ++++++ NEWS | 2 +- sysdeps/ieee754/ldbl-128ibm/s_expm1l.c | 2 ++ 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/ChangeLog b/ChangeLog index 7aa8791..f27a4eb 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2014-01-08 Joseph Myers + + [BZ #16408] + * sysdeps/ieee754/ldbl-128ibm/s_expm1l.c (__expm1l): Use __expl + for large positive arguments. + 2014-01-07 Joseph Myers * sysdeps/powerpc/nofpu/libm-test-ulps: Regenerated. diff --git a/NEWS b/NEWS index 366e1d4..486e892 100644 --- a/NEWS +++ b/NEWS @@ -24,7 +24,7 @@ Version 2.19 16103, 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, 16387, 16390, 16400, 16407. + 16384, 16385, 16386, 16387, 16390, 16400, 16407, 16408. * Slovenian translations for glibc messages have been contributed by the Translation Project's Slovenian team of translators. diff --git a/sysdeps/ieee754/ldbl-128ibm/s_expm1l.c b/sysdeps/ieee754/ldbl-128ibm/s_expm1l.c index 007e785..0464f79 100644 --- a/sysdeps/ieee754/ldbl-128ibm/s_expm1l.c +++ b/sysdeps/ieee754/ldbl-128ibm/s_expm1l.c @@ -101,6 +101,8 @@ __expm1l (long double x) EXTRACT_WORDS (ix, lx, xhi); sign = ix & 0x80000000; ix &= 0x7fffffff; + if (!sign && ix >= 0x40600000) + return __expl (x); if (ix >= 0x7ff00000) { /* Infinity. */ -- 2.7.4