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Merge pull request #42847 from ClibMouse/s390x_bit_cast

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s390x datetime64 conversion fix
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Robert Schulze 2022-11-28 11:45:43 +01:00 committed by GitHub
commit a00a020cfb
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1 changed files with 15 additions and 1 deletions
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16
base/base/bit_cast.h
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@ -12,7 +12,21 @@
template <typename To, typename From>
std::decay_t<To> bit_cast(const From & from)
{
/**
* Assume the source value is 0xAABBCCDD (i.e. sizeof(from) == 4).
* Its BE representation is 0xAABBCCDD, the LE representation is 0xDDCCBBAA.
* Further assume, sizeof(res) == 8 and that res is initially zeroed out.
* With LE, the result after bit_cast will be 0xDDCCBBAA00000000 --> input value == output value.
* With BE, the result after bit_cast will be 0x00000000AABBCCDD --> input value == output value.
*/
To res {};
memcpy(static_cast<void*>(&res), &from, std::min(sizeof(res), sizeof(from)));
if constexpr (std::endian::native == std::endian::little)
memcpy(static_cast<void*>(&res), &from, std::min(sizeof(res), sizeof(from)));
else
{
uint32_t offset_to = (sizeof(res) > sizeof(from)) ? (sizeof(res) - sizeof(from)) : 0;
uint32_t offset_from = (sizeof(from) > sizeof(res)) ? (sizeof(from) - sizeof(res)) : 0;
memcpy(reinterpret_cast<char *>(&res) + offset_to, reinterpret_cast<const char *>(&from) + offset_from, std::min(sizeof(res), sizeof(from)));
}
return res;
}