block_octree_view.hpp

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// core — device-resident view of a BlockOctree (portable Kokkos).
//
// BlockOctree (block_octree.hpp) owns the topology on the host: refine / coarsen /
// 2:1 balance rebuild its sorted leaf arrays. BlockOctreeView mirrors those
// arrays into Kokkos Views and exposes the *queries* (point location, and the
// face-neighbour step) as KOKKOS_INLINE_FUNCTIONs over the same code, so field
// kernels and the (later) octree multigrid can locate / walk leaves on device on
// any backend (CUDA / HIP / OpenMP). This mirrors the host-vs-device split the
// halo already uses (grid_halo.hpp vs grid_halo_kokkos.hpp): topology on host,
// the per-leaf hot path on device, bit-for-bit identical results.
//
// Including this header requires Kokkos (build with -DPECLET_CORE_ENABLE_KOKKOS=ON) and
// the morton sibling checkout (PECLET_CORE_HAVE_MORTON, with MORTON_ENABLE_KOKKOS so
// MORTON_HD == KOKKOS_FUNCTION).
#ifndef PECLET_CORE_AMR_BLOCK_OCTREE_VIEW_HPP
#define PECLET_CORE_AMR_BLOCK_OCTREE_VIEW_HPP
 
#ifdef PECLET_CORE_HAVE_MORTON
 
#include <cstdint>
 
#include "peclet/core/amr/block_octree.hpp"
#include "peclet/core/common/view.hpp"
 
namespace peclet::core::amr {
 
template <int Dim, unsigned Bits = (Dim == 2 ? 32u : (Dim == 3 ? 21u : 16u))>
struct BlockOctreeView {
  using Host = BlockOctree<Dim, Bits>;
  using M = typename Host::M;
  using Code = typename Host::Code;
  using Coord = typename Host::Coord;
 
  View<Code> codes;           // leaf origin codes, ascending (Z-order)
  View<std::uint8_t> levels;  // parallel to codes
  Index n = 0;
 
  void upload(const Host& t) {
    codes = toDevice(t.codes(), "amr_codes");
    levels = toDevice(t.levels(), "amr_levels");
    n = t.numLeaves();
  }
 
  Index numLeaves() const { return n; }
 
  KOKKOS_INLINE_FUNCTION Index locate(Code p) const {
    return amrLocate<M>(codes.data(), levels.data(), n, p);
  }
 
  KOKKOS_INLINE_FUNCTION Index faceNeighbor(Index i, int axis, int dir) const {
    M probe = M::from_code(codes(i));
    const Coord step = Coord(Coord(1) << levels(i));
    if (dir >= 0) {
      if (!probe.try_add(static_cast<unsigned>(axis), step))
        return -1;
    } else {
      if (!probe.try_sub(static_cast<unsigned>(axis), 1))
        return -1;
    }
    return locate(probe.code());
  }
};
 
}  // namespace peclet::core::amr
 
#endif  // PECLET_CORE_HAVE_MORTON
#endif  // PECLET_CORE_AMR_BLOCK_OCTREE_VIEW_HPP