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33 lines
1.3 KiB
C++
33 lines
1.3 KiB
C++
#pragma once
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#include <cstring>
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#include <algorithm>
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#include <type_traits>
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/** Returns value `from` converted to type `To` while retaining bit representation.
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* `To` and `From` must satisfy `CopyConstructible`.
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* In contrast to std::bit_cast can cast types of different width.
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*/
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template <typename To, typename From>
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std::decay_t<To> bit_cast(const From & from)
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{
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/**
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* Assume the source value is 0xAABBCCDD (i.e. sizeof(from) == 4).
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* Its BE representation is 0xAABBCCDD, the LE representation is 0xDDCCBBAA.
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* Further assume, sizeof(res) == 8 and that res is initially zeroed out.
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* With LE, the result after bit_cast will be 0xDDCCBBAA00000000 --> input value == output value.
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* With BE, the result after bit_cast will be 0x00000000AABBCCDD --> input value == output value.
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*/
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To res {};
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if constexpr (std::endian::native == std::endian::little)
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memcpy(static_cast<void*>(&res), &from, std::min(sizeof(res), sizeof(from)));
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else
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{
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uint32_t offset_to = (sizeof(res) > sizeof(from)) ? (sizeof(res) - sizeof(from)) : 0;
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uint32_t offset_from = (sizeof(from) > sizeof(res)) ? (sizeof(from) - sizeof(res)) : 0;
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memcpy(reinterpret_cast<char *>(&res) + offset_to, reinterpret_cast<const char *>(&from) + offset_from, std::min(sizeof(res), sizeof(from)));
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}
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return res;
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}
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