public inbox for libstdc++-cvs@sourceware.org help / color / mirror / Atom feed
From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-7597] libstdc++: Fix std::strong_order to handle NaN on VAX Date: Thu, 10 Mar 2022 14:25:57 +0000 (GMT) [thread overview] Message-ID: <20220310142557.D01B73858C20@sourceware.org> (raw) https://gcc.gnu.org/g:73f3b8a53e6664c079731c2a183c16621481d039 commit r12-7597-g73f3b8a53e6664c079731c2a183c16621481d039 Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Mar 10 14:17:03 2022 +0000 libstdc++: Fix std::strong_order to handle NaN on VAX I mistakenly believed that VAX floats do not support NaN, but with GCC __builtin_isnan(__builtin_nan("")) is true. That means my previous change to <compare> is wrong, because it fails to handle NaN. When std::numeric_limits<floating-point-type>::is_iec559 is false, as on VAX, the standard only requires an ordering that is consistent with the ordering observed by comparison operators. With this change the ordering is -NaN < numbers < +NaN, and there is no support for different NaN bit patterns (as I'm not even sure if GCC supports any for VAX). libstdc++-v3/ChangeLog: * libsupc++/compare (_Strong_order::_S_fp_cmp) [__vax__]: Handle NaN. Diff: --- libstdc++-v3/libsupc++/compare | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare index 3c22d9addf1..6e1ed53eeed 100644 --- a/libstdc++-v3/libsupc++/compare +++ b/libstdc++-v3/libsupc++/compare @@ -844,8 +844,16 @@ namespace std _S_fp_cmp(_Tp __x, _Tp __y) noexcept { #ifdef __vax__ - // VAX format has no NaN, only "excess" for Inf, so totally ordered. - return __builtin_bit_cast(strong_ordering, __x <=> __y); + if (__builtin_isnan(__x) || __builtin_isnan(__y)) + { + int __ix = (bool) __builtin_isnan(__x); + int __iy = (bool) __builtin_isnan(__y); + __ix *= __builtin_signbit(__x) ? -1 : 1; + __iy *= __builtin_signbit(__y) ? -1 : 1; + return __ix <=> __iy; + } + else + return __builtin_bit_cast(strong_ordering, __x <=> __y); #endif auto __ix = _S_fp_bits(__x);
reply other threads:[~2022-03-10 14:25 UTC|newest] Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20220310142557.D01B73858C20@sourceware.org \ --to=redi@gcc.gnu.org \ --cc=gcc-cvs@gcc.gnu.org \ --cc=libstdc++-cvs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).