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Diffstat (limited to 'extern/ceres/internal/ceres/parallel_utils.h')
-rw-r--r-- | extern/ceres/internal/ceres/parallel_utils.h | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/extern/ceres/internal/ceres/parallel_utils.h b/extern/ceres/internal/ceres/parallel_utils.h new file mode 100644 index 00000000000..1291428228a --- /dev/null +++ b/extern/ceres/internal/ceres/parallel_utils.h @@ -0,0 +1,67 @@ +// 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: wjr@google.com (William Rucklidge) + +#ifndef CERES_INTERNAL_PARALLEL_UTILS_H_ +#define CERES_INTERNAL_PARALLEL_UTILS_H_ + +namespace ceres { +namespace internal { + +// Converts a linear iteration order into a triangular iteration order. +// Suppose you have nested loops that look like +// for (int i = 0; i < n; i++) { +// for (int j = i; j < n; j++) { +// ... use i and j +// } +// } +// Naively using ParallelFor to parallelise those loops might look like +// ParallelFor(..., 0, n * n, num_threads, +// [](int thread_id, int k) { +// int i = k / n, j = k % n; +// if (j < i) return; +// ... +// }); +// but these empty work items can lead to very unbalanced threading. Instead, +// do this: +// int actual_work_items = (n * (n + 1)) / 2; +// ParallelFor(..., 0, actual_work_items, num_threads, +// [](int thread_id, int k) { +// int i, j; +// UnfoldIteration(k, n, &i, &j); +// ... +// }); +// which in each iteration will produce i and j satisfying +// 0 <= i <= j < n +void LinearIndexToUpperTriangularIndex(int k, int n, int* i, int* j); + +} // namespace internal +} // namespace ceres + +#endif // CERES_INTERNAL_PARALLEL_UTILS_H_ |