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113 lines
2.7 KiB
C++
113 lines
2.7 KiB
C++
// SPDX-License-Identifier: BSD-2-Clause
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// author: Max Kellermann <max.kellermann@gmail.com>
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#pragma once
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#include "CopyConst.hxx"
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#include <cassert>
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#include <cstddef>
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#include <span>
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#include <string_view>
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#include <type_traits>
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/**
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* Cast a std::span<std::byte> to a std::span<T>, rounding down to the
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* next multiple of T's size.
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*/
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template<typename T>
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constexpr std::span<T>
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FromBytesFloor(std::span<CopyConst<std::byte, T>> other) noexcept
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{
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static_assert(sizeof(T) > 0, "Empty base type");
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/* TODO: the "void *" cast suppresses alignment
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warnings, but should we really suppress them? */
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return {
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reinterpret_cast<T *>(reinterpret_cast<CopyConst<void, T> *>(other.data())),
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other.size() / sizeof(T),
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};
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}
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/**
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* Like FromBytesFloor(), but assert that rounding is not necessary.
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*/
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template<typename T>
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constexpr std::span<T>
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FromBytesStrict(std::span<CopyConst<std::byte, T>> other) noexcept
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{
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assert(other.size() % sizeof(T) == 0);
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return FromBytesFloor<T>(other);
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}
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constexpr std::span<const char>
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ToSpan(std::string_view sv) noexcept
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{
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#if defined(__clang__) && __clang_major__ < 15
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/* workaround for old clang/libc++ versions which can't cast
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std::string_view to std::span */
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return {sv.data(), sv.size()};
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#else
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return std::span{sv};
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#endif
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}
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inline std::span<const std::byte>
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AsBytes(std::string_view sv) noexcept
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{
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return std::as_bytes(ToSpan(sv));
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}
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/**
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* Cast a reference to a fixed-size std::span<const std::byte>.
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*/
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template<typename T>
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requires std::has_unique_object_representations_v<T>
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constexpr auto
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ReferenceAsBytes(const T &value) noexcept
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{
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return std::as_bytes(std::span<const T, 1>{&value, 1});
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}
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template<typename T>
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requires std::has_unique_object_representations_v<T>
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constexpr auto
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ReferenceAsWritableBytes(T &value) noexcept
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{
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return std::as_writable_bytes(std::span<T, 1>{&value, 1});
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}
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constexpr std::string_view
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ToStringView(std::span<const char> s) noexcept
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{
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return {s.data(), s.size()};
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}
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constexpr std::string_view
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ToStringView(std::span<const std::byte> s) noexcept
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{
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return ToStringView(FromBytesStrict<const char>(s));
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}
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template<typename T>
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requires std::is_integral_v<T>
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constexpr std::basic_string_view<std::remove_const_t<T>>
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ToStringView(std::span<T> s) noexcept
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{
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return {s.data(), s.size()};
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}
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/* this overload matches std::span<std::byte> (without "const") and is
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written that way to avoid ambiguities when passing an object that
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has cast operators for both std::span<std::byte> and
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std::span<const std::byte> */
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template<typename T>
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constexpr std::string_view
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ToStringView(std::span<T> s) noexcept
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requires(std::is_same_v<std::remove_const_t<T>, std::byte>)
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{
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return ToStringView(FromBytesStrict<const char>(s));
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}
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