broadcast.hpp

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/* This file is part of OpenKalman, a header-only C++ library for
 * Kalman filters and other recursive filters.
 *
 * Copyright (c) 2024 Christopher Lee Ogden <ogden@gatech.edu>
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#ifndef OPENKALMAN_BROADCAST_HPP
#define OPENKALMAN_BROADCAST_HPP

#include "collections/views/concat.hpp"

namespace OpenKalman
{
#ifndef __cpp_concepts
  namespace details
  {
    template<typename Factor, typename = void>
    struct FactorIs1 : std::false_type {};

    template<typename Factor>
    struct FactorIs1<Factor, std::enable_if_t<Factor::value == 1>> : std::true_type {};
  } // namespace details
#endif

#ifdef __cpp_concepts
  template<indexible Arg, values::index...Factors>
  constexpr indexible decltype(auto)
#else
  template<typename Arg, typename...Factors, std::enable_if_t<indexible<Arg> and (... and values::index<Factors>), int> = 0>
  constexpr decltype(auto)
#endif
  broadcast(Arg&& arg, const Factors&...factors)
  {
    if constexpr (sizeof...(Factors) == 0)
    {
      return std::forward<Arg>(arg);
    }
#ifdef __cpp_concepts
    else if constexpr (requires { requires std::tuple_element_t<sizeof...(Factors) - 1, std::tuple<Factors...>>::value == 1; })
#else
    else if constexpr (details::FactorIs1<std::tuple_element_t<sizeof...(Factors) - 1, std::tuple<Factors...>>>::value)
#endif
    {
      // Recursively remove any trailing 1D vector space descriptors
      return std::apply(
        [](Arg&& arg, const auto&...fs) { return broadcast(std::forward<Arg>(arg), fs...); },
        collections::views_concat(std::forward_as_tuple(std::forward<Arg>(arg)),
          internal::tuple_slice<0, sizeof...(Factors) - 1>(std::forward_as_tuple(factors...))));
    }
    else
    {
      if constexpr ((... or values::dynamic<Factors>))
      {
        if ((... or (factors <= 0))) throw std::invalid_argument {"In broadcast, all factors must be positive"};
      }

      using Trait = interface::library_interface<std::decay_t<Arg>>;
      return Trait::broadcast(std::forward<Arg>(arg), factors...);
    }
  }


} // namespace OpenKalman

#endif //OPENKALMAN_BROADCAST_HPP