* [committed] libstdc++: Support VAX floats in std::strong_order @ 2022-03-10 11:51 Jonathan Wakely 2022-03-10 12:16 ` Jonathan Wakely 0 siblings, 1 reply; 4+ messages in thread From: Jonathan Wakely @ 2022-03-10 11:51 UTC (permalink / raw) To: libstdc++, gcc-patches Tested x86_64-linux, and basic soundness check on vax-dec-netbsdelf. Pushed to trunk. -- >8 -- The VAX float and double format does not support NaN, so the std::partial_ordering returned by <=> will never be 'unordered'. We can just use the partial_ordering value as the strong_ordering. libstdc++-v3/ChangeLog: * libsupc++/compare (_Strong_ordering::_S_fp_cmp) [__vax__]: Use <=> comparison. --- libstdc++-v3/libsupc++/compare | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare index 050cf7ed20d..3c22d9addf1 100644 --- a/libstdc++-v3/libsupc++/compare +++ b/libstdc++-v3/libsupc++/compare @@ -843,6 +843,11 @@ namespace std static constexpr strong_ordering _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); +#endif + auto __ix = _S_fp_bits(__x); auto __iy = _S_fp_bits(__y); -- 2.34.1 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [committed] libstdc++: Support VAX floats in std::strong_order 2022-03-10 11:51 [committed] libstdc++: Support VAX floats in std::strong_order Jonathan Wakely @ 2022-03-10 12:16 ` Jonathan Wakely 2022-03-10 14:27 ` Jonathan Wakely 0 siblings, 1 reply; 4+ messages in thread From: Jonathan Wakely @ 2022-03-10 12:16 UTC (permalink / raw) To: Jonathan Wakely; +Cc: libstdc++, gcc Patches On Thu, 10 Mar 2022 at 11:53, Jonathan Wakely via Libstdc++ <libstdc++@gcc.gnu.org> wrote: > > Tested x86_64-linux, and basic soundness check on vax-dec-netbsdelf. But apparently not enough of a soundness check, because isnan(__builtin_nan("")) is true for VAX, so GCC seems to have a NaN pattern, despite what I read online about the format. Fix on the way ... ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [committed] libstdc++: Support VAX floats in std::strong_order 2022-03-10 12:16 ` Jonathan Wakely @ 2022-03-10 14:27 ` Jonathan Wakely 2022-03-10 17:46 ` Koning, Paul 0 siblings, 1 reply; 4+ messages in thread From: Jonathan Wakely @ 2022-03-10 14:27 UTC (permalink / raw) To: Jonathan Wakely; +Cc: libstdc++, gcc Patches [-- Attachment #1: Type: text/plain, Size: 650 bytes --] On Thu, 10 Mar 2022 at 12:16, Jonathan Wakely wrote: > > On Thu, 10 Mar 2022 at 11:53, Jonathan Wakely via Libstdc++ > <libstdc++@gcc.gnu.org> wrote: > > > > Tested x86_64-linux, and basic soundness check on vax-dec-netbsdelf. > > But apparently not enough of a soundness check, because > isnan(__builtin_nan("")) is true for VAX, so GCC seems to have a NaN > pattern, despite what I read online about the format. > > Fix on the way ... Here's the fix that adds support for VAX NaN (and works around PR104865 which I discovered while trying to make this work). Tested x86_64-linux, and slightly tested on vax-dec-netbsdelf again. Pushed to trunk. [-- Attachment #2: patch.txt --] [-- Type: text/plain, Size: 1737 bytes --] commit 73f3b8a53e6664c079731c2a183c16621481d039 Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Mar 10 14:17:03 2022 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 --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); ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [committed] libstdc++: Support VAX floats in std::strong_order 2022-03-10 14:27 ` Jonathan Wakely @ 2022-03-10 17:46 ` Koning, Paul 0 siblings, 0 replies; 4+ messages in thread From: Koning, Paul @ 2022-03-10 17:46 UTC (permalink / raw) To: Jonathan Wakely; +Cc: libstdc++, GCC Patches > On Mar 10, 2022, at 9:27 AM, Jonathan Wakely via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > On Thu, 10 Mar 2022 at 12:16, Jonathan Wakely wrote: >> >> On Thu, 10 Mar 2022 at 11:53, Jonathan Wakely via Libstdc++ >> <libstdc++@gcc.gnu.org> wrote: >>> >>> Tested x86_64-linux, and basic soundness check on vax-dec-netbsdelf. >> >> But apparently not enough of a soundness check, because >> isnan(__builtin_nan("")) is true for VAX, so GCC seems to have a NaN >> pattern, despite what I read online about the format. VAX float has signalling NaN, but not a non-signalling NaN nor an Inf. See the VAX architecture manual. Signalling NaN (called "reserved operand") is encoded as sign=1 and exponent=0. paul ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-03-10 17:46 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-03-10 11:51 [committed] libstdc++: Support VAX floats in std::strong_order Jonathan Wakely 2022-03-10 12:16 ` Jonathan Wakely 2022-03-10 14:27 ` Jonathan Wakely 2022-03-10 17:46 ` Koning, Paul
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