rng.hpp

#pragma once
 
#include <array>
#include <cstddef>
#include <cstdint>
#include <vector>
 
namespace ravel {
 
class VirtualRng {
 public:
  using Choice = std::uint64_t;
 
  explicit VirtualRng(std::uint64_t seed) noexcept;
 
  static VirtualRng replaying(std::vector<Choice> choices);
 
  std::uint64_t next_u64();
 
  std::uint64_t next_below(std::uint64_t bound);
 
  std::uint64_t next_between(std::uint64_t low, std::uint64_t high);
 
  bool chance(double probability);
 
  double next_double();
 
  const std::vector<Choice>& choices() const noexcept { return choices_; }
 
 private:
  std::uint64_t next_raw() noexcept;  
  double next_raw_double() noexcept;  
  std::uint64_t next_raw_below(std::uint64_t bound) noexcept;
 
  Choice next_replayed(std::uint64_t bound) noexcept;
 
  Choice record(Choice choice);
 
  std::array<std::uint64_t, 4> state_{};
  std::vector<Choice> choices_;
 
  bool replaying_ = false;
  std::vector<Choice> replay_;
  std::size_t replay_position_ = 0;
};
 
}  // namespace ravel