ReduceSubarraysSumCPU.h

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#pragma once

#include "tbb/parallel_for.h"

namespace open3d {
namespace ml {
namespace detail {

template <class T>
void ReduceSubarraysSumCPU(const T* const values,
                           const size_t values_size,
                           const int64_t* const prefix_sum,
                           const size_t prefix_sum_size,
                           T* out_sums) {
    tbb::parallel_for(tbb::blocked_range<size_t>(0, prefix_sum_size),
                      [&](const tbb::blocked_range<size_t>& r) {
                          for (size_t i = r.begin(); i != r.end(); ++i) {
                              size_t begin_idx = prefix_sum[i];
                              // use values_size as end_idx for the last
                              // subarray
                              size_t end_idx = (i + 1 < prefix_sum_size
                                                        ? prefix_sum[i + 1]
                                                        : values_size);

                              T sum = T(0);
                              for (size_t j = begin_idx; j < end_idx; ++j) {
                                  sum += values[j];
                              }
                              out_sums[i] = sum;
                          }
                      });
}

}  // namespace detail
}  // namespace ml
}  // namespace open3d