57 lines
1.2 KiB
C++
57 lines
1.2 KiB
C++
// Copyright (c) 2011-2016 The Cryptonote developers
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// Distributed under the MIT/X11 software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#pragma once
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#include <unordered_map>
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#include <random>
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template <typename T, typename Gen>
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class ShuffleGenerator {
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public:
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ShuffleGenerator(T n, const Gen& gen = Gen()) :
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N(n), generator(gen), count(n) {}
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T operator()() {
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if (count == 0) {
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throw std::runtime_error("shuffle sequence ended");
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}
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typedef typename std::uniform_int_distribution<T> distr_t;
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typedef typename distr_t::param_type param_t;
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distr_t distr;
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T value = distr(generator, param_t(0, --count));
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auto rvalIt = selected.find(count);
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auto rval = rvalIt != selected.end() ? rvalIt->second : count;
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auto lvalIt = selected.find(value);
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if (lvalIt != selected.end()) {
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value = lvalIt->second;
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lvalIt->second = rval;
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} else {
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selected[value] = rval;
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}
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return value;
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}
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void reset() {
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count = N;
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selected.clear();
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}
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private:
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std::unordered_map<T, T> selected;
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T count;
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const T N;
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Gen generator;
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};
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