64 lines
2.3 KiB
C
64 lines
2.3 KiB
C
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//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
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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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//
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// This file implements the C++20 <bit> header.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ADT_BIT_H
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#define LLVM_ADT_BIT_H
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#include "llvm/Support/Compiler.h"
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#include <cstring>
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#include <type_traits>
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namespace llvm {
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// This implementation of bit_cast is different from the C++17 one in two ways:
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// - It isn't constexpr because that requires compiler support.
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// - It requires trivially-constructible To, to avoid UB in the implementation.
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template <
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typename To, typename From,
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typename = std::enable_if_t<sizeof(To) == sizeof(From)>
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#if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
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(defined(__GNUC__) && __GNUC__ >= 5)
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,
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typename = std::enable_if_t<std::is_trivially_constructible<To>::value>
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#elif __has_feature(is_trivially_constructible)
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,
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typename = std::enable_if_t<__is_trivially_constructible(To)>
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#else
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// See comment below.
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#endif
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#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
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(defined(__GNUC__) && __GNUC__ >= 5)
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,
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typename = std::enable_if_t<std::is_trivially_copyable<To>::value>,
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typename = std::enable_if_t<std::is_trivially_copyable<From>::value>
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#elif __has_feature(is_trivially_copyable)
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,
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typename = std::enable_if_t<__is_trivially_copyable(To)>,
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typename = std::enable_if_t<__is_trivially_copyable(From)>
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#else
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// This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
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// llvm/Support/type_traits.h's is_trivially_copyable we don't want to
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// provide a good-enough answer here: developers in that configuration will hit
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// compilation failures on the bots instead of locally. That's acceptable
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// because it's very few developers, and only until we move past C++11.
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#endif
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>
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inline To bit_cast(const From &from) noexcept {
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To to;
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std::memcpy(&to, &from, sizeof(To));
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return to;
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}
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} // namespace llvm
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#endif
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