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+// 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
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// 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 <utility>
+
+#include "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(std::integer_sequence<int>) {
+  return true;
+}
+
+template <int N, int... Ts>
+constexpr bool IsValidParameterDimensionSequence(
+    std::integer_sequence<int, N, Ts...>) {
+  return (N <= 0) ? false
+                  : IsValidParameterDimensionSequence(
+                        std::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 = std::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<std::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, std::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_