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99 lines
1.8 KiB
C++
99 lines
1.8 KiB
C++
#pragma once
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#include <cstdint>
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#include <limits>
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#include <stdexcept>
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namespace beast {
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namespace detail {
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template <class = void>
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class XorShiftEngine
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{
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public:
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using result_type = std::uint64_t;
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XorShiftEngine(XorShiftEngine const&) = default;
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XorShiftEngine&
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operator=(XorShiftEngine const&) = default;
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explicit XorShiftEngine(result_type val = 1977u);
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void
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seed(result_type seed);
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result_type
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operator()();
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static constexpr result_type
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min()
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{
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return std::numeric_limits<result_type>::min();
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}
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static constexpr result_type
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max()
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{
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return std::numeric_limits<result_type>::max();
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}
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private:
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result_type s_[2]{};
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static result_type
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murmurhash3(result_type x);
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};
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template <class Unused>
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XorShiftEngine<Unused>::XorShiftEngine(result_type val)
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{
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seed(val);
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}
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template <class Unused>
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void
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XorShiftEngine<Unused>::seed(result_type seed)
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{
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if (seed == 0)
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throw std::domain_error("invalid seed");
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s_[0] = murmurhash3(seed);
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s_[1] = murmurhash3(s_[0]);
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}
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template <class Unused>
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auto
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XorShiftEngine<Unused>::operator()() -> result_type
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{
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result_type s1 = s_[0];
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result_type const s0 = s_[1];
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s_[0] = s0;
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s1 ^= s1 << 23;
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return (s_[1] = (s1 ^ s0 ^ (s1 >> 17) ^ (s0 >> 26))) + s0;
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}
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template <class Unused>
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auto
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XorShiftEngine<Unused>::murmurhash3(result_type x) -> result_type
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{
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x ^= x >> 33;
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x *= 0xff51afd7ed558ccdULL;
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x ^= x >> 33;
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x *= 0xc4ceb9fe1a85ec53ULL;
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return x ^= x >> 33;
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}
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} // namespace detail
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/** XOR-shift Generator.
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Meets the requirements of UniformRandomNumberGenerator.
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Simple and fast RNG based on:
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http://xorshift.di.unimi.it/xorshift128plus.c
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does not accept seed==0
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*/
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using xor_shift_engine = detail::XorShiftEngine<>;
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} // namespace beast
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