93 lines
2.2 KiB
C++
93 lines
2.2 KiB
C++
// SPDX-FileCopyrightText: 2005-2014 Daniel James
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// SPDX-FileCopyrightText: 2016 Austin Appleby
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// SPDX-License-Identifier: BSL-1.0
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#include <array>
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#include <climits>
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#include <cstdint>
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#include <limits>
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#include <type_traits>
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#include <vector>
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namespace Common {
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namespace detail {
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template <typename T>
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requires std::is_unsigned_v<T>
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inline std::size_t HashValue(T val) {
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const unsigned int size_t_bits = std::numeric_limits<std::size_t>::digits;
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const unsigned int length =
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(std::numeric_limits<T>::digits - 1) / static_cast<unsigned int>(size_t_bits);
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std::size_t seed = 0;
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for (unsigned int i = length * size_t_bits; i > 0; i -= size_t_bits) {
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seed ^= static_cast<size_t>(val >> i) + (seed << 6) + (seed >> 2);
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}
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seed ^= static_cast<size_t>(val) + (seed << 6) + (seed >> 2);
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return seed;
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}
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template <size_t Bits>
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struct HashCombineImpl {
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template <typename T>
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static inline T fn(T seed, T value) {
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seed ^= value + 0x9e3779b9 + (seed << 6) + (seed >> 2);
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return seed;
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}
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};
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template <>
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struct HashCombineImpl<64> {
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static inline std::uint64_t fn(std::uint64_t h, std::uint64_t k) {
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const std::uint64_t m = (std::uint64_t(0xc6a4a793) << 32) + 0x5bd1e995;
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const int r = 47;
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k *= m;
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k ^= k >> r;
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k *= m;
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h ^= k;
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h *= m;
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// Completely arbitrary number, to prevent 0's
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// from hashing to 0.
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h += 0xe6546b64;
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return h;
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}
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};
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} // namespace detail
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template <typename T>
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inline void HashCombine(std::size_t& seed, const T& v) {
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seed = detail::HashCombineImpl<sizeof(std::size_t) * CHAR_BIT>::fn(seed, detail::HashValue(v));
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}
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template <typename It>
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inline std::size_t HashRange(It first, It last) {
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std::size_t seed = 0;
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for (; first != last; ++first) {
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HashCombine<typename std::iterator_traits<It>::value_type>(seed, *first);
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}
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return seed;
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}
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template <typename T, size_t Size>
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std::size_t HashValue(const std::array<T, Size>& v) {
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return HashRange(v.cbegin(), v.cend());
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}
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template <typename T, typename Allocator>
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std::size_t HashValue(const std::vector<T, Allocator>& v) {
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return HashRange(v.cbegin(), v.cend());
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}
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} // namespace Common
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