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[77.0.40.57]) by smtp.gmail.com with ESMTPSA id b17-20020a170906491100b009adc81bb544sm3016878ejq.106.2023.10.04.08.54.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Oct 2023 08:54:41 -0700 (PDT) Message-ID: <097e48f1-b915-4d6c-b68e-8ee282bc6de5@redhat.com> Date: Wed, 4 Oct 2023 17:54:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [committed] libstdc++: Define std::numeric_limits<_FloatNN> before C++23 To: Jonathan Wakely , libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org References: <20230817203213.1131496-1-jwakely@redhat.com> Cc: Pranav Kant From: Stephan Bergmann In-Reply-To: <20230817203213.1131496-1-jwakely@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-10.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,KAM_NUMSUBJECT,KAM_SHORT,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 8/17/23 22:32, Jonathan Wakely via Libstdc++ wrote: > Tested x86_64-linux. Pushed to trunk. > > -- >8 -- > > The extended floating-point types such as _Float32 are supported by GCC > prior to C++23, you just can't use the standard-conforming names from > to refer to them. This change defines the specializations of > std::numeric_limits for those types for older dialects, not only for > C++23. > > libstdc++-v3/ChangeLog: > > * include/bits/c++config (__gnu_cxx::__bfloat16_t): Define > whenever __BFLT16_DIG__ is defined, not only for C++23. > * include/std/limits (numeric_limits): Likewise. > (numeric_limits<_Float16>, numeric_limits<_Float32>) > (numeric_limits<_Float64>): Likewise for other extended > floating-point types. > --- > libstdc++-v3/include/bits/c++config | 4 +- > libstdc++-v3/include/std/limits | 194 +++++++++++++++------------- > 2 files changed, 103 insertions(+), 95 deletions(-) > [...] > diff --git a/libstdc++-v3/include/std/limits b/libstdc++-v3/include/std/limits > index 52b19ef8264..7a59e7520eb 100644 > --- a/libstdc++-v3/include/std/limits > +++ b/libstdc++-v3/include/std/limits > @@ -1890,189 +1890,197 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION [...] > __glibcxx_float_n(64) > #endif > -#ifdef __STDCPP_FLOAT128_T__ > +#ifdef __FLT128_DIG__ > __glibcxx_float_n(128) > #endif > #undef __glibcxx_float_n [...] The above change (from __STDCPP_FLOAT128_T__ to __FLT128_DIG__) now started to cause issues with Clang on Clang 18 trunk: * Clang does not support a _Float128 type. * Clang does not predefine __STDCPP_FLOAT128_T__. * But since "[clang] Predefined macros for float128 support (#67196)", Clang 18 trunk does predefine __FLT128_DIG__ now. Which causes > $ cat test.cc > #include > $ clang++ -fsyntax-only test.cc > In file included from test.cc:1: > /home/sbergman/gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/14.0.0/../../../../include/c++/14.0.0/limits:1995:1: error: use of undeclared identifier '_Float128' > 1995 | __glibcxx_float_n(128) > | ^ > /home/sbergman/gcc/trunk/inst/lib/gcc/x86_64-pc-linux-gnu/14.0.0/../../../../include/c++/14.0.0/limits:1903:27: note: expanded from macro '__glibcxx_float_n' > 1903 | struct numeric_limits<_Float##BITSIZE> \ > | ^ > :36:1: note: expanded from here > 36 | _Float128 > | ^ > 1 error generated. (I don't know whether or not it is useful for Clang to predefine __FLT128_DIG__ when not providing a _Float128 type. I assume "ISO/IEC TS 18661-3:2015", as referenced by the C++ standard, might be relevant here, but don't know that document. I added Pranav, the author of the relevant Clang commit, in cc here.)