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As discussed on cfe-dev [1], use the using_if_exists Clang attribute when the compiler supports it. This makes it easier to port libc++ on top of new platforms that don't fully support the C Standard library. Previously, libc++ would fail to build when trying to import a missing declaration in a <cXXXX> header. With the attribute, the declaration will simply not be imported into namespace std, and hence it won't be available for libc++ to use. In many cases, the declarations were *not* actually required for libc++ to work (they were only surfaced for users to use them as std::XXXX), so not importing them into namespace std is acceptable. The same thing could be achieved by conscious usage of `#ifdef` along with platform detection, however that quickly creates a maintenance problem as libc++ is ported to new platforms. Furthermore, this problem is exacerbated when mixed with vendor internal-only platforms, which can lead to difficulties maintaining a downstream fork of the library. For the time being, we only use the using_if_exists attribute when it is supported. At some point in the future, we will start removing #ifdef paths that are unnecessary when the attribute is supported, and folks who need those #ifdef paths will be required to use a compiler that supports the attribute. [1]: http://lists.llvm.org/pipermail/cfe-dev/2020-June/066038.html Differential Revision: https://reviews.llvm.org/D90257
82 lines
1.9 KiB
C++
82 lines
1.9 KiB
C++
// -*- C++ -*-
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//===---------------------------- cfenv -----------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP_CFENV
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#define _LIBCPP_CFENV
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/*
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cfenv synopsis
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This entire header is C99 / C++0X
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Macros:
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FE_DIVBYZERO
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FE_INEXACT
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FE_INVALID
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FE_OVERFLOW
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FE_UNDERFLOW
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FE_ALL_EXCEPT
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FE_DOWNWARD
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FE_TONEAREST
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FE_TOWARDZERO
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FE_UPWARD
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FE_DFL_ENV
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namespace std
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{
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Types:
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fenv_t
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fexcept_t
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int feclearexcept(int excepts);
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int fegetexceptflag(fexcept_t* flagp, int excepts);
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int feraiseexcept(int excepts);
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int fesetexceptflag(const fexcept_t* flagp, int excepts);
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int fetestexcept(int excepts);
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int fegetround();
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int fesetround(int round);
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int fegetenv(fenv_t* envp);
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int feholdexcept(fenv_t* envp);
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int fesetenv(const fenv_t* envp);
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int feupdateenv(const fenv_t* envp);
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} // std
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*/
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#include <__config>
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#include <fenv.h>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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#pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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using ::fenv_t _LIBCPP_USING_IF_EXISTS;
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using ::fexcept_t _LIBCPP_USING_IF_EXISTS;
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using ::feclearexcept _LIBCPP_USING_IF_EXISTS;
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using ::fegetexceptflag _LIBCPP_USING_IF_EXISTS;
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using ::feraiseexcept _LIBCPP_USING_IF_EXISTS;
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using ::fesetexceptflag _LIBCPP_USING_IF_EXISTS;
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using ::fetestexcept _LIBCPP_USING_IF_EXISTS;
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using ::fegetround _LIBCPP_USING_IF_EXISTS;
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using ::fesetround _LIBCPP_USING_IF_EXISTS;
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using ::fegetenv _LIBCPP_USING_IF_EXISTS;
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using ::feholdexcept _LIBCPP_USING_IF_EXISTS;
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using ::fesetenv _LIBCPP_USING_IF_EXISTS;
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using ::feupdateenv _LIBCPP_USING_IF_EXISTS;
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP_CFENV
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