cpp-shared-random-generator/src/random.cxx

#include "random/random.h"

#include <cassert>
#include <cfloat>
#include <random>

#include <scope_guard/scope_guard.hpp>

#include "random/device.h"
#include "random/distribution.h"
#include "random/tape.h"

#define IMPLEMENT_RANDOM(T)                                                    \
  template T Random::operator()(Distribution<T> const &) const;

namespace engine::random {
class DefaultDevice : public Device {
public:
  result_type operator()() final { return rng(); }

private:
  std::mt19937 rng{std::random_device{}()};
};

Random::Random() : impl_(std::make_shared<DefaultDevice>()) {}

Random::Random(Random const & other, std::shared_ptr<Tape> with_tape)
    : impl_(other.impl_), tape_(with_tape) {}

Random::Random(Random const & other, Tape & with_tape)
    : impl_(other.impl_), tape_(&with_tape, [](void *) {}) {}

template <typename Rand>
Rand Random::operator()(Distribution<Rand> const & dist) const {
  return tape_ ? tape_->apply(dist, impl_->apply(dist)) : impl_->apply(dist);
}

scope_exit Random::record(std::shared_ptr<Tape> tape) {
  assert(tape && !tape_);
  tape_ = tape;
  return [this]() { tape_.reset(); };
}

IMPLEMENT_DEVICE(IMPLEMENT_RANDOM)
}