memoizer.hh

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#ifndef __BASE_MEMOIZER_HH__
#define __BASE_MEMOIZER_HH__
 
#include <functional>
#include <map>
#include <type_traits>
#include <utility>
 
namespace gem5
{
 
template <typename Ret, typename... Args>
class Memoizer
{
  public:
    using ret_type = Ret;
    using args_type = std::tuple<Args...>;
 
    constexpr Memoizer(Ret _func(Args...))
     : func(_func)
    {
        validateMemoizer();
    }
 
    Memoizer() = delete;
    Memoizer(const Memoizer &rhs) = delete;
    Memoizer& operator=(const Memoizer &rhs) = delete;
 
    auto
    operator()(Args... args) const
    {
        auto key = std::make_tuple(args...);
        if (auto it = cache.find(key); it != cache.end()) {
            // Return the cached result
            return it->second;
        }
        auto emplaced = cache.emplace(key, func(args...));
        return emplaced.first->second;
    };
 
    void flush() { cache.clear(); }
 
  protected:
    bool
    cached(args_type args) const
    {
        return cache.find(args) != cache.end();
    }
 
    size_t
    cacheSize() const
    {
        return cache.size();
    }
 
  private:
    constexpr void
    validateMemoizer()
    {
        constexpr size_t num_args = std::tuple_size_v<std::decay_t<args_type>>;
        iterateTupleArgs<size_t(0), num_args, size_t(1)>([&](auto i) {
            static_assert(!std::is_reference_v<
                typename std::tuple_element<
                    i.value, args_type>::type>);
        });
    }
 
    template <size_t Start, size_t End, size_t Inc, class F>
    constexpr void
    iterateTupleArgs(F&& func)
    {
        if constexpr (Start < End) {
            func(std::integral_constant<decltype(Start), Start>());
            iterateTupleArgs<Start + Inc, End, Inc>(func);
        }
    }
 
  private:
    const std::function<Ret(Args...)> func;
    mutable std::map<args_type, ret_type> cache;
 
};
 
} // namespace gem5
 
#endif // __BASE_MEMOIZER_HH__