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51 lines
1.0 KiB
51 lines
1.0 KiB
4 years ago
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#pragma once
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#include <cstdint>
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namespace devilution {
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/**
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* @brief A tagged union of a pointer and a value in the space of a single pointer.
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*
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* Requires the type T to have alignment > 1.
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* Internally, uses the last bit to hold the tag:
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* 0 if it is a pointer, guaranteed by T's alignment requirements.
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* 1 if it is a value.
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*/
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template <typename T>
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class PointerOrValue {
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static_assert(alignof(T) > 1, "requires alignof > 1");
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static_assert(sizeof(T) < sizeof(T *), "type too large");
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public:
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explicit PointerOrValue(const T *ptr)
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: repr_(reinterpret_cast<uintptr_t>(ptr))
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{
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}
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explicit PointerOrValue(T val)
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: repr_((static_cast<uintptr_t>(val) << 1) | 1)
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{
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}
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[[nodiscard]] bool HoldsPointer() const
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{
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return (repr_ & 1) == 0;
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}
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[[nodiscard]] const T *AsPointer() const
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{
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return reinterpret_cast<const T *>(repr_);
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}
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[[nodiscard]] T AsValue() const
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{
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return repr_ >> 1;
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}
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private:
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uintptr_t repr_;
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};
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} // namespace devilution
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