bb34568af2
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
51 lines
1.4 KiB
C++
51 lines
1.4 KiB
C++
#pragma once
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#include <mbgl/util/ignore.hpp>
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#include <functional>
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#include <type_traits>
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namespace mbgl {
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namespace util {
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template <class T>
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void hash_combine(std::size_t& seed, const T& v) noexcept {
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seed ^= std::hash<T>()(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
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}
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template <class... Args>
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std::size_t hash(Args&&... args) noexcept {
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std::size_t seed = 0;
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ignore({(hash_combine(seed, args), 0)...});
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return seed;
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}
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namespace detail {
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template <typename TIter>
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using TIterVal = std::enable_if_t<std::is_integral_v<typename TIter::value_type>, typename TIter::value_type>;
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} // namespace detail
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template <typename T>
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constexpr T factor() noexcept {
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// Default factor prime value from 64-bit FNV hash.
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if constexpr (sizeof(T) == 8) return 1099511628211;
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// for 32-bit hash
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return 16777619;
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}
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/// Generate a hash key from a collection of integer values which doesn't depend on their order.
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/// Adapted from https://stackoverflow.com/a/76993810/135138
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template <typename TIter, typename TKey = detail::TIterVal<TIter>, TKey factor = factor<TKey>()>
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TKey order_independent_hash(std::remove_const_t<TIter> cur, const TIter end) noexcept {
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detail::TIterVal<TIter> sum = 0, product = 1;
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for (; cur != end; ++cur) {
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const auto& value = *cur;
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sum += value;
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product *= (1 + value) * factor;
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}
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return sum ^ product;
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}
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} // namespace util
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} // namespace mbgl
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