mirror of
https://github.com/ceres-solver/ceres-solver.git
synced 2026-08-29 16:40:38 +08:00
Johannes Beck
336a6be5a4
This PR adds integer sequence and two algorithms (sum and exclusive scan). Those will be needed to implement a sized cost function using variadic templates. Change-Id: I8e98d7c11fac94286fe9c364633406e59438f059
107 lines
4.3 KiB
C++
107 lines
4.3 KiB
C++
// Ceres Solver - A fast non-linear least squares minimizer
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// Copyright 2018 Google Inc. All rights reserved.
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// http://ceres-solver.org/
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// * Redistributions of source code must retain the above copyright notice,
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// this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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// * Neither the name of Google Inc. nor the names of its contributors may be
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// used to endorse or promote products derived from this software without
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// specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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// POSSIBILITY OF SUCH DAMAGE.
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//
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// Author: jodebo_beck@gmx.de (Johannes Beck)
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//
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// This class mimics std::integer_sequence. That is the reason to follow the
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// naming convention of the stl and not the google one. Once Ceres switches
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// to c++ 14 this class can be removed.
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#ifndef CERES_PUBLIC_INTERNAL_INTEGER_SEQUENCE_H_
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#define CERES_PUBLIC_INTERNAL_INTEGER_SEQUENCE_H_
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#if __cplusplus >= 201402L
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// We have at least c++ 14 support. Use integer_sequence from the standard.
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// Sometimes the STL implementation uses a compiler intrinsic to generate
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// the sequences which will speed up compilation.
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#include <utility>
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namespace ceres {
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namespace internal {
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template <typename T, T... Ns>
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using integer_sequence = std::integer_sequence<T, Ns...>;
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template <typename T, T N>
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using make_integer_sequence = std::make_integer_sequence<T, N>;
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} // namespace internal
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} // namespace ceres
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#else
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namespace ceres {
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namespace internal {
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template <typename T, T... Ns>
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struct integer_sequence {
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using value_type = T;
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};
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// Implementation of make_integer_sequence.
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//
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// Recursively instantiate make_integer_sequence_impl until Ns
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// contains the sequence 0, 1, ..., Total-1.
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//
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// Example for Total = 4:
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// T CurIdx, Total, Ns...
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// make_integer_sequence_impl<int, 0, 4 >
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// make_integer_sequence_impl<int, 1, 4, 0 >
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// make_integer_sequence_impl<int, 2, 4, 0, 1 >
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// make_integer_sequence_impl<int, 3, 4, 0, 1, 2 >
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// make_integer_sequence_impl<int, 4, 4, 0, 1, 2, 3>
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// ^^^^^^^^^^
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// resulting sequence.
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//
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// The implemented algorithm has linear complexity for simplicity. A O(log(N))
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// implementation can be found e.g. here:
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// https://stackoverflow.com/questions/17424477/implementation-c14-make-integer-sequence
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template <typename T, T CurIdx, T Total, T... Ns>
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struct make_integer_sequence_impl {
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using type = typename make_integer_sequence_impl<T, CurIdx + 1, Total, Ns...,
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CurIdx>::type;
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};
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// End of 'recursion' when CurIdx reaches Total. All indices 0, 1, ..., N-1 are
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// contained in Ns. The final integer_sequence is created here.
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template <typename T, T Total, T... Ns>
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struct make_integer_sequence_impl<T, Total, Total, Ns...> {
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using type = integer_sequence<T, Ns...>;
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};
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// A helper alias template to simplify creation of integer_sequence with 0, 1,
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// ..., N-1 as Ns:
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template <typename T, T N>
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using make_integer_sequence =
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typename make_integer_sequence_impl<T, 0, N>::type;
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} // namespace internal
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} // namespace ceres
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#endif
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#endif // CERES_PUBLIC_INTERNAL_INTEGER_SEQUENCE_H_
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