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From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug math/16620] [ldbl-128ibm] exp10l spurious overflows / bad directed rounding results Date: Wed, 30 Sep 2015 23:36:00 -0000 [thread overview] Message-ID: <bug-16620-131-xSC25rbkX0@http.sourceware.org/bugzilla/> (raw) In-Reply-To: <bug-16620-131@http.sourceware.org/bugzilla/> https://sourceware.org/bugzilla/show_bug.cgi?id=16620 --- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> --- This is an automated email from the git hooks/post-receive script. It was generated because a ref change was pushed to the repository containing the project "GNU C Library master sources". The branch, master has been updated via 7cda516f5f23772fd37ca3a5e018fca5bf388435 (commit) from 8c6c9236361fbc077769673c259828216403bc33 (commit) Those revisions listed above that are new to this repository have not appeared on any other notification email; so we list those revisions in full, below. - Log ----------------------------------------------------------------- https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7cda516f5f23772fd37ca3a5e018fca5bf388435 commit 7cda516f5f23772fd37ca3a5e018fca5bf388435 Author: Joseph Myers <joseph@codesourcery.com> Date: Wed Sep 30 23:34:59 2015 +0000 Fix ldbl-128ibm exp10l spurious overflows (bug 16620). The ldbl-128ibm implementation of exp10l uses a version of log(10) split into high and low parts - but the low part is negative, so causing spurious overflows from __ieee754_expl (exp_high) in cases close to the overflow threshold (I added relevant tests close to the overflow threshold to the testsuite earlier today). The same issue applies close to the underflow threshold as well (except that spurious underflows in IBM long double arithmetic are harder to fix than the other deficiencies, so we might end up permitting those for IBM long double in the libm testsuite, as permitted by ISO C). This patch fixes it to use a low part rounded downward to 48 bits instead. (The choice of 48 instead of 53 bits is to make it more obviously safe even when the low part of the argument is negative.) Tested for powerpc. (Note that because of libgcc bugs with multiplication very close to LDBL_MAX, libgcc also needs patching for all the problem cases to be fixed, but this patch is still safe and correct in the absence of such libgcc fixes.) [BZ #16620] * sysdeps/ieee754/ldbl-128ibm/e_exp10l.c (log10_high): Use value of log (10) rounded downward to 48 bits. (log10_low): Use corresponding low part of log (10). ----------------------------------------------------------------------- Summary of changes: ChangeLog | 5 +++++ NEWS | 16 ++++++++-------- sysdeps/ieee754/ldbl-128ibm/e_exp10l.c | 4 ++-- 3 files changed, 15 insertions(+), 10 deletions(-) -- You are receiving this mail because: You are on the CC list for the bug.
next prev parent reply other threads:[~2015-09-30 23:36 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-02-21 2:19 [Bug math/16620] New: " jsm28 at gcc dot gnu.org 2014-06-13 8:10 ` [Bug math/16620] " fweimer at redhat dot com 2015-09-30 23:36 ` cvs-commit at gcc dot gnu.org [this message] 2015-09-30 23:37 ` jsm28 at gcc dot gnu.org
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