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/*
* Frozen
* Copyright 2016 QuarksLab
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
#ifndef FROZEN_LETITGO_RANDOM_H
#define FROZEN_LETITGO_RANDOM_H
#include "frozen/bits/algorithms.h"
#include "frozen/bits/version.h"
#include <cstdint>
#include <type_traits>
namespace frozen {
template <class UIntType, UIntType a, UIntType c, UIntType m>
class linear_congruential_engine {
static_assert(std::is_unsigned<UIntType>::value,
"UIntType must be an unsigned integral type");
template<class T>
static constexpr UIntType modulo(T val, std::integral_constant<UIntType, 0>) {
return static_cast<UIntType>(val);
}
template<class T, UIntType M>
static constexpr UIntType modulo(T val, std::integral_constant<UIntType, M>) {
// the static cast below may end up doing a truncation
return static_cast<UIntType>(val % M);
}
public:
using result_type = UIntType;
static constexpr result_type multiplier = a;
static constexpr result_type increment = c;
static constexpr result_type modulus = m;
static constexpr result_type default_seed = 1u;
linear_congruential_engine() = default;
constexpr linear_congruential_engine(result_type s) { seed(s); }
void seed(result_type s = default_seed) { state_ = s; }
constexpr result_type operator()() {
using uint_least_t = bits::select_uint_least_t<bits::log(a) + bits::log(m) + 4>;
uint_least_t tmp = static_cast<uint_least_t>(multiplier) * state_ + increment;
state_ = modulo(tmp, std::integral_constant<UIntType, modulus>());
return state_;
}
constexpr void discard(unsigned long long n) {
while (n--)
operator()();
}
static constexpr result_type min() { return increment == 0u ? 1u : 0u; }
static constexpr result_type max() { return modulus - 1u; }
friend constexpr bool operator==(linear_congruential_engine const &self,
linear_congruential_engine const &other) {
return self.state_ == other.state_;
}
friend constexpr bool operator!=(linear_congruential_engine const &self,
linear_congruential_engine const &other) {
return !(self == other);
}
private:
result_type state_ = default_seed;
};
using minstd_rand0 =
linear_congruential_engine<std::uint_fast32_t, 16807, 0, 2147483647>;
using minstd_rand =
linear_congruential_engine<std::uint_fast32_t, 48271, 0, 2147483647>;
// This generator is used by default in unordered frozen containers
using default_prg_t = minstd_rand;
} // namespace frozen
#endif
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