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64 lines
2.5 KiB
C++
64 lines
2.5 KiB
C++
//
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// AccessType.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/11/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace InstructionSet::x86 {
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/// Explains the type of access that `perform` intends to perform; is provided as a template parameter to whatever
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/// the caller supplies as `MemoryT` and `RegistersT` when obtaining a reference to whatever the processor
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/// intends to reference.
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///
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/// `perform` guarantees to validate all accesses before modifying any state, giving the caller opportunity to generate
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/// any exceptions that might be applicable.
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enum class AccessType {
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/// The requested value will be read from.
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Read,
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/// The requested value will be written to.
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Write,
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/// The requested value will be read from and then written to.
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ReadModifyWrite,
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/// The requested value has already been authorised for whatever form of access is now intended, so there's no
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/// need further to inspect. This is done e.g. by operations that will push multiple values to the stack to verify that
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/// all necessary stack space is available ahead of pushing anything, though each individual push will then result in
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/// a further `Preauthorised` access.
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PreauthorisedRead,
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};
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constexpr bool is_writeable(AccessType type) {
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return type == AccessType::ReadModifyWrite || type == AccessType::Write;
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}
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template <typename IntT, AccessType type> struct Accessor;
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// Reads: return a value directly.
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template <typename IntT> struct Accessor<IntT, AccessType::Read> { using type = IntT; };
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template <typename IntT> struct Accessor<IntT, AccessType::PreauthorisedRead> { using type = IntT; };
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// Writes: return a custom type that can be written but not read.
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template <typename IntT>
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class Writeable {
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public:
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Writeable(IntT &target) : target_(target) {}
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IntT operator=(IntT value) { return target_ = value; }
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private:
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IntT &target_;
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};
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template <typename IntT> struct Accessor<IntT, AccessType::Write> { using type = Writeable<IntT>; };
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// Read-modify-writes: return a reference.
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template <typename IntT> struct Accessor<IntT, AccessType::ReadModifyWrite> { using type = IntT &; };
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// Shorthands; assumed that preauthorised reads have the same return type as reads.
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template<typename IntT> using read_t = typename Accessor<IntT, AccessType::Read>::type;
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template<typename IntT> using write_t = typename Accessor<IntT, AccessType::Write>::type;
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template<typename IntT> using modify_t = typename Accessor<IntT, AccessType::ReadModifyWrite>::type;
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template<typename IntT, AccessType type> using access_t = typename Accessor<IntT, type>::type;
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}
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