text: // Ceres Solver - A fast non-linear least squares minimizer
  // Copyright 2018 Google Inc. All rights reserved.
  // http://ceres-solver.org/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are met:
  //
  // * Redistributions of source code must retain the above copyright notice,
  //   this list of conditions and the following disclaimer.
  // * Redistributions in binary form must reproduce the above copyright notice,
  //   this list of conditions and the following disclaimer in the documentation
  //   and/or other materials provided with the distribution.
  // * Neither the name of Google Inc. nor the names of its contributors may be
  //   used to endorse or promote products derived from this software without
  //   specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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  // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  // POSSIBILITY OF SUCH DAMAGE.
  //
  // Author: jodebo_beck@gmx.de (Johannes Beck)
  
  #ifndef CERES_PUBLIC_INTERNAL_PARAMETER_DIMS_H_
  #define CERES_PUBLIC_INTERNAL_PARAMETER_DIMS_H_
  
  #include <array>
  
  #include "AutodiffCodegen/ceres/internal/integer_sequence.h"
  #include "AutodiffCodegen/ceres/internal/integer_sequence_algorithm.h"
  
  namespace ceres {
  namespace internal {
  
  // Checks, whether the given parameter block sizes are valid. Valid means every
  // dimension is bigger than zero.
  constexpr bool IsValidParameterDimensionSequence(integer_sequence<int>) {
    return true;
  }
  
  template <int N, int... Ts>
  constexpr bool IsValidParameterDimensionSequence(
      integer_sequence<int, N, Ts...>) {
    return (N <= 0) ? false
                    : IsValidParameterDimensionSequence(
                          integer_sequence<int, Ts...>());
  }
  
  // Helper class that represents the parameter dimensions. The parameter
  // dimensions are either dynamic or the sizes are known at compile time. It is
  // used to pass parameter block dimensions around (e.g. between functions or
  // classes).
  //
  // As an example if one have three parameter blocks with dimensions (2, 4, 1),
  // one would use 'StaticParameterDims<2, 4, 1>' which is a synonym for
  // 'ParameterDims<false, 2, 4, 1>'.
  // For dynamic parameter dims, one would just use 'DynamicParameterDims', which
  // is a synonym for 'ParameterDims<true>'.
  template <bool IsDynamic, int... Ns>
  class ParameterDims {
   public:
    using Parameters = integer_sequence<int, Ns...>;
  
    // The parameter dimensions are only valid if all parameter block dimensions
    // are greater than zero.
    static constexpr bool kIsValid =
        IsValidParameterDimensionSequence(Parameters());
    static_assert(kIsValid,
                  "Invalid parameter block dimension detected. Each parameter "
                  "block dimension must be bigger than zero.");
  
    static constexpr bool kIsDynamic = IsDynamic;
    static constexpr int kNumParameterBlocks = sizeof...(Ns);
    static_assert(kIsDynamic || kNumParameterBlocks > 0,
                  "At least one parameter block must be specified.");
  
    static constexpr int kNumParameters =
        Sum<integer_sequence<int, Ns...>>::Value;
  
    static constexpr int GetDim(int dim) { return params_[dim]; }
  
    // If one has all parameters packed into a single array this function unpacks
    // the parameters.
    template <typename T>
    static inline std::array<T*, kNumParameterBlocks> GetUnpackedParameters(
        T* ptr) {
      using Offsets = ExclusiveScan<Parameters>;
      return GetUnpackedParameters(ptr, Offsets());
    }
  
   private:
    template <typename T, int... Indices>
    static inline std::array<T*, kNumParameterBlocks> GetUnpackedParameters(
        T* ptr, integer_sequence<int, Indices...>) {
      return std::array<T*, kNumParameterBlocks>{{ptr + Indices...}};
    }
  
    static constexpr std::array<int, kNumParameterBlocks> params_{Ns...};
  };
  
  // Even static constexpr member variables needs to be defined (not only
  // declared). As the ParameterDims class is tempalted this definition must
  // be in the header file.
  template <bool IsDynamic, int... Ns>
  constexpr std::array<int, ParameterDims<IsDynamic, Ns...>::kNumParameterBlocks>
      ParameterDims<IsDynamic, Ns...>::params_;
  
  // Using declarations for static and dynamic parameter dims. This makes client
  // code easier to read.
  template <int... Ns>
  using StaticParameterDims = ParameterDims<false, Ns...>;
  using DynamicParameterDims = ParameterDims<true>;
  
  }  // namespace internal
  }  // namespace ceres
  
  #endif  // CERES_PUBLIC_INTERNAL_PARAMETER_DIMS_H_
  