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ba87515fea
Currently, the library-internal feature test macros are only defined if the feature is not available, and always have the prefix `_LIBCPP_HAS_NO_`. This patch changes that, so that they are always defined and have the prefix `_LIBCPP_HAS_` instead. This changes the canonical use of these macros to `#if _LIBCPP_HAS_FEATURE`, which means that using an undefined macro (e.g. due to a missing include) is diagnosed now. While this is rather unlikely currently, a similar change in `<__configuration/availability.h>` caught a few bugs. This also improves readability, since it removes the double-negation of `#ifndef _LIBCPP_HAS_NO_FEATURE`. The current patch only touches the macros defined in `<__config>`. If people are happy with this approach, I'll make a follow-up PR to also change the macros defined in `<__config_site>`.
54 lines
1.6 KiB
C++
54 lines
1.6 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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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___BIT_BYTESWAP_H
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#define _LIBCPP___BIT_BYTESWAP_H
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#include <__concepts/arithmetic.h>
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#include <__config>
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#include <cstdint>
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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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#if _LIBCPP_STD_VER >= 23
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template <integral _Tp>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
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if constexpr (sizeof(_Tp) == 1) {
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return __val;
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} else if constexpr (sizeof(_Tp) == 2) {
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return __builtin_bswap16(__val);
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} else if constexpr (sizeof(_Tp) == 4) {
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return __builtin_bswap32(__val);
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} else if constexpr (sizeof(_Tp) == 8) {
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return __builtin_bswap64(__val);
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# if _LIBCPP_HAS_INT128
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} else if constexpr (sizeof(_Tp) == 16) {
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# if __has_builtin(__builtin_bswap128)
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return __builtin_bswap128(__val);
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# else
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return static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val))) << 64 |
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static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val >> 64)));
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# endif // __has_builtin(__builtin_bswap128)
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# endif // _LIBCPP_HAS_INT128
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} else {
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static_assert(sizeof(_Tp) == 0, "byteswap is unimplemented for integral types of this size");
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}
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}
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#endif // _LIBCPP_STD_VER >= 23
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___BIT_BYTESWAP_H
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