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diff --git a/extern/ceres/internal/ceres/parallel_for_openmp.cc b/extern/ceres/internal/ceres/parallel_for_openmp.cc
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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: vitus@google.com (Michael Vitus)
+
+// This include must come before any #ifndef check on Ceres compile options.
+#include "ceres/internal/port.h"
+
+#if defined(CERES_USE_OPENMP)
+
+#include "ceres/parallel_for.h"
+
+#include "ceres/scoped_thread_token.h"
+#include "ceres/thread_token_provider.h"
+#include "glog/logging.h"
+#include "omp.h"
+
+namespace ceres {
+namespace internal {
+
+int MaxNumThreadsAvailable() {
+  return omp_get_max_threads();
+}
+
+void ParallelFor(ContextImpl* context,
+                 int start,
+                 int end,
+                 int num_threads,
+                 const std::function<void(int)>& function) {
+  CHECK_GT(num_threads, 0);
+  CHECK(context != NULL);
+  if (end <= start) {
+    return;
+  }
+
+#ifdef CERES_USE_OPENMP
+#pragma omp parallel for num_threads(num_threads) \
+    schedule(dynamic) if (num_threads > 1)
+#endif  // CERES_USE_OPENMP
+  for (int i = start; i < end; ++i) {
+    function(i);
+  }
+}
+
+void ParallelFor(ContextImpl* context,
+                 int start,
+                 int end,
+                 int num_threads,
+                 const std::function<void(int thread_id, int i)>& function) {
+  CHECK(context != NULL);
+
+  ThreadTokenProvider thread_token_provider(num_threads);
+  ParallelFor(context, start, end, num_threads, [&](int i) {
+    const ScopedThreadToken scoped_thread_token(&thread_token_provider);
+    const int thread_id = scoped_thread_token.token();
+    function(thread_id, i);
+  });
+}
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // defined(CERES_USE_OPENMP)