53 lines
1.6 KiB
C
53 lines
1.6 KiB
C
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#include <tuple>
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// function has to live in the std namespace
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// so that it is picked up by argument-dependent name lookup (ADL).
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namespace std{
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namespace
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{
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// Code from boost
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// Reciprocal of the golden ratio helps spread entropy
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// and handles duplicates.
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// See Mike Seymour in magic-numbers-in-boosthash-combine:
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// https://stackoverflow.com/questions/4948780
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template <class T>
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inline void hash_combine(std::size_t& seed, T const& v)
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{
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seed ^= hash<T>()(v) + 0x9e3779b9 + (seed<<6) + (seed>>2);
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}
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// Recursive template code derived from Matthieu M.
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template <class Tuple, size_t Index = std::tuple_size<Tuple>::value - 1>
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struct HashValueImpl
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{
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static void apply(size_t& seed, Tuple const& tuple)
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{
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HashValueImpl<Tuple, Index-1>::apply(seed, tuple);
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hash_combine(seed, get<Index>(tuple));
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}
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};
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template <class Tuple>
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struct HashValueImpl<Tuple,0>
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{
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static void apply(size_t& seed, Tuple const& tuple)
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{
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hash_combine(seed, get<0>(tuple));
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}
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};
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}
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template <typename ... TT>
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struct hash<std::tuple<TT...>>
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{
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size_t
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operator()(std::tuple<TT...> const& tt) const
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{
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size_t seed = 0;
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HashValueImpl<std::tuple<TT...> >::apply(seed, tt);
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return seed;
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}
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};
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}
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