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From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug math/16354] cosh spurious underflows Date: Mon, 23 Jun 2014 20:21:00 -0000 [thread overview] Message-ID: <bug-16354-131-r2XHzQ7QPR@http.sourceware.org/bugzilla/> (raw) In-Reply-To: <bug-16354-131@http.sourceware.org/bugzilla/> https://sourceware.org/bugzilla/show_bug.cgi?id=16354 --- 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 4648909d56c1e9063017bcddd3271dffadef7cb5 (commit) from 46a3d3c7d60db15ea65470800bcba695f55ce6f6 (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=4648909d56c1e9063017bcddd3271dffadef7cb5 commit 4648909d56c1e9063017bcddd3271dffadef7cb5 Author: Joseph Myers <joseph@codesourcery.com> Date: Mon Jun 23 20:20:10 2014 +0000 Fix cosh spurious underflows from expm1 (bug 16354), inaccurate results near 0 (bug 17061). This patch fixes bug 16354, spurious underflows from cosh when a tiny argument is passed to expm1 and expm1 correctly underflows although the final result of cosh should be 1. As noted in that bug, some cases are latent because of expm1 implementations not raising underflow (bug 16353), but all the implementations are fixed similarly. They already contained checks for tiny arguments, but the checks were too late to avoid underflow from expm1 (although they would avoid underflow from subsequent squaring of the result of expm1); they are moved before the expm1 calls. The thresholds used for considering arguments tiny are not particularly consistent in how they relate to the precision of the floating-point format in question. They are, however, all sufficient to ensure that the round-to-nearest result of cosh is indeed 1 below the threshold (although sometimes they are smaller than necessary). But the previous logic did not return 1, but the previously computed 1 + expm1(abs(x)) value. And the thresholds in the ldbl-128 and ldbl-128ibm code (0x1p-71L - I suspect 0x3f8b was intended in the code instead of 0x3fb8 - and (roughly) 0x1p-55L) are not sufficient for that value to be 1. So by moving the test for tiny arguments, and consequently returning 1 directly now the expm1 value hasn't been computed by that point, this patch also fixes bug 17061, the (large number of ulps) inaccuracy for small arguments in those implementations. Tests for that bug are duly added. Tested x86_64 and x86 and ulps updated accordingly. Also tested for mips64 and powerpc32 to validate the ldbl-128 and ldbl-128ibm changes. [BZ #16354] [BZ #17061] * sysdeps/ieee754/dbl-64/e_cosh.c (__ieee754_cosh): Check for small arguments before calling __expm1. * sysdeps/ieee754/flt-32/e_coshf.c (__ieee754_coshf): Check for small arguments before calling __expm1f. * sysdeps/ieee754/ldbl-128/e_coshl.c (__ieee754_coshl): Check for small arguments before calling __expm1l. * sysdeps/ieee754/ldbl-128ibm/e_coshl.c (__ieee754_coshl): Likewise. * sysdeps/ieee754/ldbl-96/e_coshl.c (__ieee754_coshl): Likewise. * math/auto-libm-test-in: Add more cosh tests. Do not allow spurious underflow for some cosh tests. * math/auto-libm-test-out: Regenerated. * sysdeps/i386/fpu/libm-test-ulps: Update. ----------------------------------------------------------------------- Summary of changes: ChangeLog | 16 + NEWS | 20 +- math/auto-libm-test-in | 13 +- math/auto-libm-test-out | 732 +++++++++++++++++++-------------- sysdeps/i386/fpu/libm-test-ulps | 1 + sysdeps/ieee754/dbl-64/e_cosh.c | 4 +- sysdeps/ieee754/flt-32/e_coshf.c | 2 +- sysdeps/ieee754/ldbl-128/e_coshl.c | 4 +- sysdeps/ieee754/ldbl-128ibm/e_coshl.c | 2 +- sysdeps/ieee754/ldbl-96/e_coshl.c | 2 +- 10 files changed, 458 insertions(+), 338 deletions(-) -- You are receiving this mail because: You are on the CC list for the bug.
next prev parent reply other threads:[~2014-06-23 20:21 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-12-20 18:11 [Bug math/16354] New: " jsm28 at gcc dot gnu.org 2014-06-13 11:23 ` [Bug math/16354] " fweimer at redhat dot com 2014-06-23 20:21 ` cvs-commit at gcc dot gnu.org [this message] 2014-06-23 20:21 ` jsm28 at gcc dot gnu.org 2015-06-22 21:07 ` cvs-commit at gcc dot gnu.org
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