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FNV-1a hashing a wide-string with multiple of 4 length in chunks of 64-bits
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constexpr auto hash_64bitwise(std::wstring_view str) noexcept | |
{ | |
using SizeType = decltype(str)::size_type; | |
constexpr auto offset_basis = 0xcbf29ce484222325ull; | |
constexpr auto prime = 0x00000100000001B3ull; | |
auto value = offset_basis; | |
auto size = str.length(); | |
if (size % 4) | |
return 0ull; | |
for (SizeType i{}; i < size / 4; ++i) { | |
std::uint64_t chunk = 0; | |
if (std::is_constant_evaluated()) { | |
chunk = []<std::size_t... Is>(wchar_t const *ptr, std::index_sequence<Is...>) constexpr { | |
return ((static_cast<std::uint64_t>(ptr[Is]) << (16u * Is)) | ...); | |
}(&str[(i * 4)], std::make_index_sequence<4>{}); | |
} else { | |
std::memcpy(&chunk, &str[i * 4], 8); | |
} | |
value = (value ^ chunk) * prime; | |
} | |
return value; | |
} |
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