AMReX_Box.H

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#ifndef AMREX_BOX_H_
#define AMREX_BOX_H_
#include <AMReX_Config.H>
 
#include <AMReX_Algorithm.H>
#include <AMReX_ArrayLim.H>
#include <AMReX_BoxIterator.H>
#include <AMReX_ccse-mpi.H>
#include <AMReX_IntVect.H>
#include <AMReX_IndexType.H>
#include <AMReX_Orientation.H>
#include <AMReX_SPACE.H>
#include <AMReX_Array.H>
#include <AMReX_Array4.H>
#include <AMReX_Vector.H>
#include <AMReX_GpuQualifiers.H>
#include <AMReX_GpuControl.H>
#include <AMReX_Math.H>
 
#include <iosfwd>

 
namespace amrex
{
template<int dim>
class BoxND;
using Box = BoxND<AMREX_SPACEDIM>;
class BoxCommHelper;
template<int dim>
class BoxIteratorND;

template<int dim>
class BoxND
{
    friend MPI_Datatype ParallelDescriptor::Mpi_typemap<Box>::type();
    friend class BoxCommHelper;
 
public:
    // DO NOT CHANGE THIS BEHAVIOR!
    AMREX_GPU_HOST_DEVICE
    constexpr BoxND () noexcept
        : smallend(1),
          bigend(0)
        {}

    AMREX_GPU_HOST_DEVICE
    constexpr BoxND (const IntVectND<dim>& small, const IntVectND<dim>& big) noexcept
        : smallend(small),
          bigend(big)
        {}

    AMREX_GPU_HOST_DEVICE
    BoxND (const IntVectND<dim>& small, const int* vec_len) noexcept
        : smallend(small),
          bigend(small + IntVectND<dim>(vec_len) - 1)
        {}

    AMREX_GPU_HOST_DEVICE
    BoxND (const IntVectND<dim>& small, const IntVectND<dim>& big, const IntVectND<dim>& typ) noexcept
        : smallend(small),
          bigend(big),
          btype(typ)
        {
            BL_ASSERT(typ.allGE(0) && typ.allLE(1));
        }

    AMREX_GPU_HOST_DEVICE
    BoxND (const IntVectND<dim>& small, const IntVectND<dim>& big, IndexTypeND<dim> t) noexcept
        : smallend(small),
          bigend(big),
          btype(t)
        {}

    template <typename T>
    requires ( 1<=dim && dim<=3 )
    AMREX_GPU_HOST_DEVICE
    explicit BoxND (Array4<T> const& a) noexcept
        : smallend(IntVectShrink<dim>(a.begin)),
          bigend(IntVectShrink<dim>(a.end) - 1)
        {}
 
    // dtor, copy-ctor, copy-op=, move-ctor, and move-op= are compiler generated.

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    const IntVectND<dim>& smallEnd () const& noexcept { return smallend; }

    [[nodiscard]] const IntVectND<dim>& smallEnd () && = delete;

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int smallEnd (int dir) const& noexcept { return smallend[dir]; }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    const IntVectND<dim>& bigEnd () const& noexcept { return bigend; }

    [[nodiscard]] const IntVectND<dim>& bigEnd () && = delete;

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int bigEnd (int dir) const noexcept { return bigend[dir]; }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    IndexTypeND<dim> ixType () const noexcept { return btype; }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    IntVectND<dim> type () const noexcept { return btype.ixType(); }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    IndexType::CellIndex type (int dir) const noexcept { return btype.ixType(dir); }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    IntVectND<dim> size () const noexcept
    {
        return bigend - smallend + 1;
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    IntVectND<dim> length () const noexcept
    {
        return bigend - smallend + 1;
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int length (int dir) const noexcept { return bigend[dir] - smallend[dir] + 1; }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    GpuArray<int,3> length3d () const noexcept
        requires (1 <= dim && dim <= 3)
    {
        Dim3 len3d = length().dim3(1);
        return {{len3d.x, len3d.y, len3d.z}};
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    GpuArray<int,3> loVect3d () const noexcept
        requires (1 <= dim && dim <= 3)
    {
        Dim3 lo3d = smallend.dim3(0);
        return {{lo3d.x, lo3d.y, lo3d.z}};
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    GpuArray<int,3> hiVect3d () const noexcept
        requires (1 <= dim && dim <= 3)
    {
        Dim3 hi3d = bigend.dim3(0);
        return {{hi3d.x, hi3d.y, hi3d.z}};
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    const int* loVect () const& noexcept { return smallend.getVect(); }
    AMREX_GPU_HOST_DEVICE
    const int* loVect () && = delete;
    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    const int* hiVect () const& noexcept { return bigend.getVect(); }
    AMREX_GPU_HOST_DEVICE
    const int* hiVect () && = delete;

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int operator[] (Orientation face) const noexcept {
        const int dir = face.coordDir();
        return face.isLow() ? smallend[dir] : bigend[dir];
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool isEmpty () const noexcept { return !ok(); }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool ok () const noexcept { return bigend.allGE(smallend) && btype.ok(); }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool contains (const IntVectND<dim>& p) const noexcept {
        return p.allGE(smallend) && p.allLE(bigend);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool contains (const Dim3& p) const noexcept
        requires (1 <= dim && dim <= 3)
    {
        IntVectND<dim> piv{p};
        return contains(piv);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool contains (int i, int j, int k) const noexcept
        requires (1 <= dim && dim <= 3)
    {
        Dim3 p3d{.x = i, .y = j, .z = k};
        return contains(p3d);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool contains (const BoxND& b) const noexcept
    {
        BL_ASSERT(sameType(b));
        return b.smallend.allGE(smallend) && b.bigend.allLE(bigend);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool strictly_contains (const IntVectND<dim>& p) const noexcept {
        return p.allGT(smallend) && p.allLT(bigend);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool strictly_contains (const BoxND& b) const noexcept
    {
        BL_ASSERT(sameType(b));
        return b.smallend.allGT(smallend) && b.bigend.allLT(bigend);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool strictly_contains (const Dim3& p) const noexcept
        requires (1 <= dim && dim <= 3)
    {
        IntVectND<dim> piv{p};
        return strictly_contains(piv);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool strictly_contains (int i, int j, int k) const noexcept
        requires (1 <= dim && dim <= 3)
    {
        Dim3 p3d{.x = i, .y = j, .z = k};
        return strictly_contains(p3d);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool intersects (const BoxND& b) const noexcept { BoxND isect(*this); isect &= b; return isect.ok(); }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool sameSize (const BoxND& b) const noexcept {
        BL_ASSERT(sameType(b));
        return length() == b.length();
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool sameType (const BoxND &b) const noexcept { return btype == b.btype; }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool operator== (const BoxND& b) const noexcept { return smallend == b.smallend && bigend == b.bigend && b.btype == btype; }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool operator!= (const BoxND& b) const noexcept { return !operator==(b); }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool operator< (const BoxND& rhs) const noexcept
    {
        return btype < rhs.btype ||
             ((btype == rhs.btype) &&
                 (  (smallend < rhs.smallend) ||
                   ((smallend == rhs.smallend) && (bigend < rhs.bigend)) ));
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool operator <= (const BoxND& rhs) const noexcept {
        return !(rhs < *this);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool operator> (const BoxND& rhs) const noexcept {
        return rhs < *this;
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool operator>= (const BoxND& rhs) const noexcept {
        return !(*this < rhs);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool cellCentered () const noexcept { return !btype.any(); }

    void checkOverflow () const {
        if (ok()) {
            for (int i = 0; i < dim; ++i) {
                auto lo = static_cast<Long>(smallend[i]);
                auto hi = static_cast<Long>(bigend[i]);
                Long len = hi - lo + 1;
                AMREX_ALWAYS_ASSERT_WITH_MESSAGE(len>=0 && len<std::numeric_limits<int>::max(),
                    "Overflow when computing length of box");
            }
            auto num_pts = static_cast<Long>(length(0));
            for (int i = 1; i < dim; ++i) {
                auto len = static_cast<Long>(length(i));
                AMREX_ALWAYS_ASSERT_WITH_MESSAGE(num_pts == 0 || len == 0 ||
                    num_pts <= std::numeric_limits<Long>::max() / len,
                    "Overflow when computing numPts of box");
                num_pts *= len;
            }
        }
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    Long numPts () const noexcept {
#if defined(AMREX_DEBUG) || defined(AMREX_USE_ASSERTION)
        AMREX_IF_ON_HOST((checkOverflow();))
#endif
        if (ok()) {
            auto num_pts = static_cast<Long>(length(0));
            for (int i = 1; i < dim; ++i) {
                num_pts *= static_cast<Long>(length(i));
            }
            return num_pts;
        } else {
            return Long(0);
        }
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    double d_numPts () const noexcept {
        if (ok()) {
            auto num_pts = static_cast<double>(length(0));
            for (int i = 1; i < dim; ++i) {
                num_pts *= static_cast<double>(length(i));
            }
            return num_pts;
        } else {
            return 0.0;
        }
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    Long volume () const noexcept {
        if (ok()) {
            auto num_pts = static_cast<Long>(length(0)-btype[0]);
            for (int i = 1; i < dim; ++i) {
                num_pts *= static_cast<Long>(length(i)-btype[i]);
            }
            return num_pts;
        } else {
            return Long(0);
        }
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int longside (int& dir) const noexcept {
        int maxlen = length(0);
        dir = 0;
        for (int i = 1; i < dim; i++)
        {
            if (length(i) > maxlen)
            {
                maxlen = length(i);
                dir = i;
            }
        }
        return maxlen;
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int longside () const noexcept {
        int ignore = 0;
        return longside(ignore);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int shortside (int& dir) const noexcept {
        int minlen = length(0);
        dir = 0;
        for (int i = 1; i < dim; i++)
        {
            if (length(i) < minlen)
            {
                minlen = length(i);
                dir = i;
            }
        }
        return minlen;
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    int shortside () const noexcept {
        int ignore = 0;
        return shortside(ignore);
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    Long index (const IntVectND<dim>& v) const noexcept;

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    IntVectND<dim> atOffset (Long offset) const noexcept;

    template <int N=dim>
    requires (1 <= N && N <= 3)
    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    GpuArray<int,3> atOffset3d (Long offset) const noexcept;
 
    AMREX_GPU_HOST_DEVICE
    BoxND& setSmall (const IntVectND<dim>& sm) noexcept { smallend = sm; return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& setSmall (int dir, int sm_index) noexcept { smallend.setVal(dir,sm_index); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& setBig (const IntVectND<dim>& bg) noexcept { bigend = bg; return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& setBig (int dir, int bg_index) noexcept { bigend.setVal(dir,bg_index); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& setRange (int dir,
                   int sm_index,
                   int n_cells = 1) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& setType (const IndexTypeND<dim>& t) noexcept { btype = t; return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& shift (int dir, int nzones) noexcept { smallend.shift(dir,nzones); bigend.shift(dir,nzones); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& shift (const IntVectND<dim>& iv) noexcept { smallend.shift(iv); bigend.shift(iv); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& shiftHalf (int dir, int num_halfs) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& shiftHalf (const IntVectND<dim>& iv) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& convert (IndexTypeND<dim> typ) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& convert (const IntVectND<dim>& typ) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& surroundingNodes () noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& surroundingNodes (int dir) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& surroundingNodes (Direction d) noexcept { return surroundingNodes(static_cast<int>(d)); }

    AMREX_GPU_HOST_DEVICE
    BoxND& enclosedCells () noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& enclosedCells (int dir) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& enclosedCells (Direction d) noexcept { return enclosedCells(static_cast<int>(d)); }

    AMREX_GPU_HOST_DEVICE
    BoxND operator& (const BoxND& rhs) const noexcept { BoxND lhs(*this); lhs &= rhs; return lhs; }

    AMREX_GPU_HOST_DEVICE
    BoxND& operator&= (const BoxND& rhs) noexcept
    {
        BL_ASSERT(sameType(rhs));
        smallend.max(rhs.smallend);
        bigend.min(rhs.bigend);
        return *this;
    }

    AMREX_GPU_HOST_DEVICE
    BoxND& minBox (const BoxND& b) noexcept {
        // BoxArray may call this with not ok boxes.  BL_ASSERT(b.ok() && ok());
        BL_ASSERT(sameType(b));
        smallend.min(b.smallend);
        bigend.max(b.bigend);
        return *this;
    }

    AMREX_GPU_HOST_DEVICE
    BoxND& operator+= (const IntVectND<dim>& v) noexcept { smallend += v; bigend   += v; return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND operator+ (const IntVectND<dim>& v) const noexcept { BoxND r(*this); r += v; return r; }

    AMREX_GPU_HOST_DEVICE
    BoxND& operator-= (const IntVectND<dim>& v) noexcept { smallend -= v; bigend -= v; return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND operator- (const IntVectND<dim>& v) const noexcept { BoxND r(*this); r -= v; return r; }

    AMREX_GPU_HOST_DEVICE
    BoxND chop (int dir, int chop_pnt) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& grow (int i) noexcept { smallend.diagShift(-i); bigend.diagShift(i); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& grow (const IntVectND<dim>& v) noexcept { smallend -= v; bigend += v; return *this;}

    AMREX_GPU_HOST_DEVICE
    BoxND& grow (int idir, int n_cell) noexcept { smallend.shift(idir, -n_cell); bigend.shift(idir, n_cell); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& grow (Direction d, int n_cell) noexcept { return grow(static_cast<int>(d), n_cell); }

    AMREX_GPU_HOST_DEVICE
    BoxND& growLo (int idir, int n_cell = 1) noexcept { smallend.shift(idir, -n_cell); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& growLo (Direction d, int n_cell = 1) noexcept { return growLo(static_cast<int>(d), n_cell); }

    AMREX_GPU_HOST_DEVICE
    BoxND& growHi (int idir, int n_cell = 1) noexcept { bigend.shift(idir,n_cell); return *this; }

    AMREX_GPU_HOST_DEVICE
    BoxND& growHi (Direction d, int n_cell = 1) noexcept { return growHi(static_cast<int>(d), n_cell); }

    AMREX_GPU_HOST_DEVICE
    BoxND& grow (Orientation face, int n_cell = 1) noexcept {
        int idir = face.coordDir();
        if (face.isLow()) {
            smallend.shift(idir, -n_cell);
        } else {
            bigend.shift(idir,n_cell);
        }
        return *this;
    }

    AMREX_GPU_HOST_DEVICE
    BoxND& refine (int ref_ratio) noexcept {
        return this->refine(IntVectND<dim>(ref_ratio));
    }

    AMREX_GPU_HOST_DEVICE
    BoxND& refine (const IntVectND<dim>& ref_ratio) noexcept;

    AMREX_GPU_HOST_DEVICE
    BoxND& coarsen (int ref_ratio) noexcept {
        return this->coarsen(IntVectND<dim>(ref_ratio));
    }

    AMREX_GPU_HOST_DEVICE
    BoxND& coarsen (const IntVectND<dim>& ref_ratio) noexcept;

    AMREX_GPU_HOST_DEVICE
    void next (IntVectND<dim> &) const noexcept;

    AMREX_GPU_HOST_DEVICE
    static BoxND TheUnitBox () noexcept {
        return BoxND(IntVectND<dim>::TheZeroVector(),IntVectND<dim>::TheZeroVector());
    }
 
    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool isSquare() const noexcept;

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool coarsenable (const IntVectND<dim>& refrat, const IntVectND<dim>& min_width) const noexcept
    {
        if (!size().allGE(refrat*min_width)) {
            return false;
        } else {
            BoxND testBox = *this;
            testBox.coarsen(refrat);
            testBox.refine (refrat);
            return (*this == testBox);
        }
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool coarsenable (int refrat, int min_width=1) const noexcept {
        return coarsenable(IntVectND<dim>(refrat), IntVectND<dim>(min_width));
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE
    bool coarsenable (const IntVectND<dim>& refrat, int min_width=1) const noexcept
    {
        return coarsenable(refrat, IntVectND<dim>(min_width));
    }

    AMREX_GPU_HOST_DEVICE
    void normalize () noexcept
    {
        for (int idim=0; idim < dim; ++idim) {
            if (this->length(idim) == 0) {
                this->growHi(idim,1);
            }
        }
    }

    AMREX_GPU_HOST_DEVICE
    BoxND& makeSlab (int direction, int slab_index) noexcept
    {
        smallend[direction] = slab_index;
        bigend[direction] = slab_index;
        return *this;
    }

    [[nodiscard]] BoxIteratorND<dim> iterator () const noexcept {
        return BoxIteratorND<dim>{*this};
    }
 
    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    static constexpr std::size_t ndims () noexcept {
        return static_cast<std::size_t>(dim);
    }
 
    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    static constexpr int indims () noexcept {
        return dim;
    }

    template<int new_dim>
    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    BoxND<new_dim> shrink () const noexcept {
        static_assert(new_dim <= dim);
        auto lo = smallend.template shrink<new_dim>();
        auto hi = bigend.template shrink<new_dim>();
        auto typ = btype.template shrink<new_dim>();
        return BoxND<new_dim>(lo, hi, typ);
    }

    template<int new_dim>
    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    BoxND<new_dim> expand () const noexcept {
        static_assert(new_dim >= dim);
        auto lo = smallend.template expand<new_dim>(0);
        auto hi = bigend.template expand<new_dim>(0);
        auto typ = btype.template expand<new_dim>(IndexType::CellIndex::CELL);
        return BoxND<new_dim>(lo, hi, typ);
    }

    template<int new_dim>
    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    BoxND<new_dim> resize () const noexcept {
        if constexpr (new_dim > dim) {
            return expand<new_dim>();
        } else {
            return shrink<new_dim>();
        }
    }
 
private:
    IntVectND<dim>         smallend;
    IntVectND<dim>         bigend;
    IndexTypeND<dim>       btype;
};
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::refine (const IntVectND<dim>& ref_ratio) noexcept
{
    if (ref_ratio != 1) {
        IntVectND<dim> shft(1);
        shft -= btype.ixType();
        smallend *= ref_ratio;
        bigend += shft;
        bigend *= ref_ratio;
        bigend -= shft;
    }
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::coarsen (const IntVectND<dim>& ref_ratio) noexcept
{
    if (ref_ratio != 1)
    {
        smallend.coarsen(ref_ratio);
 
        if (btype.any())
        {
            IntVectND<dim> off(0);
            for (int dir = 0; dir < dim; dir++)
            {
                if (btype[dir]) {
                    if (bigend[dir]%ref_ratio[dir]) {
                        off.setVal(dir,1);
                    }
                }
            }
            bigend.coarsen(ref_ratio);
            bigend += off;
        }
        else
        {
            bigend.coarsen(ref_ratio);
        }
    }
 
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::convert (const IntVectND<dim>& typ) noexcept
{
    BL_ASSERT(typ.allGE(0) && typ.allLE(1));
    IntVectND<dim> shft(typ - btype.ixType());
    bigend += shft;
    btype = IndexTypeND<dim>(typ);
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::convert (IndexTypeND<dim> t) noexcept
{
   for (int dir = 0; dir < dim; dir++)
   {
      const auto typ = t[dir];
      const auto bitval = btype[dir];
      const int off = typ - bitval;
      bigend.shift(dir,off);
      btype.setType(dir, static_cast<IndexType::CellIndex>(typ));
   }
   return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::surroundingNodes (int dir) noexcept
{
    if (!(btype[dir]))
    {
        bigend.shift(dir,1);
        //
        // Set dir'th bit to 1 = IndexType::NODE.
        //
        btype.set(dir);
    }
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::surroundingNodes () noexcept
{
    for (int i = 0; i < dim; ++i) {
        if ((btype[i] == 0)) {
            bigend.shift(i,1);
        }
    }
    btype.setall();
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::enclosedCells (int dir) noexcept
{
    if (btype[dir])
    {
        bigend.shift(dir,-1);
        //
        // Set dir'th bit to 0 = IndexType::CELL.
        //
        btype.unset(dir);
    }
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::enclosedCells () noexcept
{
    for (int i = 0 ; i < dim; ++i) {
        if (btype[i]) {
            bigend.shift(i,-1);
        }
    }
    btype.clear();
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Long
BoxND<dim>::index (const IntVectND<dim>& v) const noexcept
{
    IntVectND<dim> vz = v - smallend;
    Long result = vz[0];
    Long mult = length(0);
    for (int i = 1 ; i < dim; ++i) {
        result += mult * vz[i];
        mult *= length(i);
    }
    return result;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim>
BoxND<dim>::atOffset (Long offset) const noexcept
{
    IntVectND<dim> result = smallend;
 
    if constexpr (dim > 1) {
        GpuArray<Long, dim-1> mult{};
        mult[0] = length(0);
        for (int i = 1 ; i < dim-1; ++i) {
            mult[i] = mult[i-1] * length(i);
        }
        for (int i = dim-1 ; i > 0; --i) {
            Long idx = offset / mult[i-1];
            offset -= idx * mult[i-1];
            result[i] += static_cast<int>(idx);
        }
    }
 
    result[0] += static_cast<int>(offset);
 
    return result;
}
 
template<int dim>
template <int N>
requires (1 <= N && N <= 3)
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
GpuArray<int,3>
BoxND<dim>::atOffset3d (Long offset) const noexcept
{
    Dim3 iv3d = atOffset(offset).dim3(0);
    return {{iv3d.x, iv3d.y, iv3d.z}};
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim>&
BoxND<dim>::setRange (int dir,
               int sm_index,
               int n_cells) noexcept
{
    smallend.setVal(dir,sm_index);
    bigend.setVal(dir,sm_index+n_cells-1);
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
void
BoxND<dim>::next (IntVectND<dim>& p) const noexcept // NOLINT(readability-convert-member-functions-to-static)
{
    BL_ASSERT(contains(p));
 
    ++p[0];
 
    for (int i = 0 ; i < dim-1; ++i) {
        if (p[i] > bigend[i]) {
            p[i] = smallend[i];
            ++p[i+1];
        } else {
            break;
        }
    }
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
bool
BoxND<dim>::isSquare () const noexcept // NOLINT(readability-convert-member-functions-to-static)
{
    if constexpr (dim == 1) {
        return false; // can't build a square in 1-D
    } else {
        bool is_square = true;
        const IntVectND<dim>& sz = this->size();
        for (int i = 0 ; i < dim-1; ++i) {
            is_square = is_square && (sz[i] == sz[i+1]);
        }
        return is_square;
    }
}
 
//
// Modified BoxND is low end, returned BoxND is high end.
// If CELL: chop_pnt included in high end.
// If NODE: chop_pnt included in both Boxes.
//
 
template<int dim>
AMREX_GPU_HOST_DEVICE
inline
BoxND<dim>
BoxND<dim>::chop (int dir, int chop_pnt) noexcept
{
    //
    // Define new high end BoxND including chop_pnt.
    //
    IntVectND<dim> sm(smallend);
    IntVectND<dim> bg(bigend);
    sm.setVal(dir,chop_pnt);
    if (btype[dir])
    {
        //
        // NODE centered BoxND.
        //
        BL_ASSERT(chop_pnt > smallend[dir] && chop_pnt < bigend[dir]);
        //
        // Shrink original BoxND to just contain chop_pnt.
        //
        bigend.setVal(dir,chop_pnt);
    }
    else
    {
        //
        // CELL centered BoxND.
        //
        BL_ASSERT(chop_pnt > smallend[dir] && chop_pnt <= bigend[dir]);
        //
        // Shrink original BoxND to one below chop_pnt.
        //
        bigend.setVal(dir,chop_pnt-1);
    }
    return BoxND<dim>(sm,bg,btype);
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
inline
BoxND<dim>&
BoxND<dim>::shiftHalf (int dir, int num_halfs) noexcept
{
    const int nbit = (num_halfs<0 ? -num_halfs : num_halfs)%2;
    int nshift = num_halfs/2;
    //
    // Toggle btyp bit if num_halfs is odd.
    //
    const unsigned int bit_dir = btype[dir];
    if (nbit) {
        btype.flip(dir);
    }
    if (num_halfs < 0) {
        nshift -= (bit_dir ? nbit : 0);
    } else {
        nshift += (bit_dir ? 0 : nbit);
    }
    smallend.shift(dir,nshift);
    bigend.shift(dir,nshift);
    return *this;
}
 
template<int dim>
AMREX_GPU_HOST_DEVICE
inline
BoxND<dim>&
BoxND<dim>::shiftHalf (const IntVectND<dim>& iv) noexcept
{
    for (int i = 0; i < dim; i++) {
        shiftHalf(i,iv[i]);
    }
    return *this;
}

class BoxCommHelper
{
public:
 
    explicit BoxCommHelper (const Box& bx, int* p_ = nullptr);
 
    [[nodiscard]] int* data () const& noexcept { return p; }
    int* data () && = delete;
 
    [[nodiscard]] Box make_box () const noexcept {
        return Box(IntVect(p), IntVect(p+AMREX_SPACEDIM), IntVect(p+2*AMREX_SPACEDIM));
    }
 
    [[nodiscard]] static int size () noexcept { return 3*AMREX_SPACEDIM; }
 
private:
    int* p;
    std::vector<int> v;
};
 
class BoxConverter { // NOLINT
public:
    virtual Box doit (const Box& fine) const = 0; // NOLINT
    virtual BoxConverter* clone () const = 0; // NOLINT
    [[nodiscard]] virtual bool equals (const BoxConverter& other) const = 0;
    virtual ~BoxConverter () = default;
};

void AllGatherBoxes (Vector<Box>& bxs, int n_extra_reserve=0);

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> grow (const BoxND<dim>& b, int i) noexcept
{
    BoxND<dim> result = b;
    result.grow(i);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> grow (const BoxND<dim>& b, const IntVectND<dim>& v) noexcept
{
    BoxND<dim> result = b;
    result.grow(v);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> grow (const BoxND<dim>& b, int idir, int n_cell) noexcept
{
    BoxND<dim> result = b;
    result.grow(idir, n_cell);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> grow (const BoxND<dim>& b, Direction d, int n_cell) noexcept
{
    return grow(b, static_cast<int>(d), n_cell);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> growLo (const BoxND<dim>& b, int idir, int n_cell) noexcept
{
    BoxND<dim> result = b;
    result.growLo(idir, n_cell);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> growLo (const BoxND<dim>& b, Direction d, int n_cell) noexcept
{
    return growLo(b, static_cast<int>(d), n_cell);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> growHi (const BoxND<dim>& b, int idir, int n_cell) noexcept
{
    BoxND<dim> result = b;
    result.growHi(idir, n_cell);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> growHi (const BoxND<dim>& b, Direction d, int n_cell) noexcept
{
    return growHi(b, static_cast<int>(d), n_cell);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> coarsen (const BoxND<dim>& b, int ref_ratio) noexcept
{
    BoxND<dim> result = b;
    result.coarsen(IntVectND<dim>(ref_ratio));
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> coarsen (const BoxND<dim>& b, const IntVectND<dim>& ref_ratio) noexcept
{
    BoxND<dim> result = b;
    result.coarsen(ref_ratio);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> refine (const BoxND<dim>& b, int ref_ratio) noexcept
{
    BoxND<dim> result = b;
    result.refine(IntVectND<dim>(ref_ratio));
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> refine (const BoxND<dim>& b, const IntVectND<dim>& ref_ratio) noexcept
{
    BoxND<dim> result = b;
    result.refine(ref_ratio);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> shift (const BoxND<dim>& b, int dir, int nzones) noexcept
{
    BoxND<dim> result = b;
    result.shift(dir, nzones);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> shift (const BoxND<dim>& b, const IntVectND<dim>& nzones) noexcept
{
    BoxND<dim> result = b;
    result.shift(nzones);
    return result;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> surroundingNodes (const BoxND<dim>& b, int dir) noexcept
{
    BoxND<dim> bx(b);
    bx.surroundingNodes(dir);
    return bx;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> surroundingNodes (const BoxND<dim>& b, Direction d) noexcept
{
    return surroundingNodes(b, static_cast<int>(d));
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> surroundingNodes (const BoxND<dim>& b) noexcept
{
    BoxND<dim> bx(b);
    bx.surroundingNodes();
    return bx;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> convert (const BoxND<dim>& b, const IntVectND<dim>& typ) noexcept
{
    BoxND<dim> bx(b);
    bx.convert(typ);
    return bx;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> convert (const BoxND<dim>& b, const IndexTypeND<dim>& typ) noexcept
{
    BoxND<dim> bx(b);
    bx.convert(typ);
    return bx;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> enclosedCells (const BoxND<dim>& b, int dir) noexcept
{
    BoxND<dim> bx(b);
    bx.enclosedCells(dir);
    return bx;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> enclosedCells (const BoxND<dim>& b, Direction d) noexcept
{
    return enclosedCells(b, static_cast<int>(d));
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> enclosedCells (const BoxND<dim>& b) noexcept
{
    BoxND<dim> bx(b);
    bx.enclosedCells();
    return bx;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> bdryLo (const BoxND<dim>& b, int dir, int len=1) noexcept
{
    IntVectND<dim> low(b.smallEnd());
    IntVectND<dim> hi(b.bigEnd());
    int sm = low[dir];
    low.setVal(dir,sm-len+1);
    hi.setVal(dir,sm);
    //
    // set dir'th bit to 1 = IndexType::NODE.
    //
    IndexTypeND<dim> typ(b.ixType());
    typ.set(dir);
    return BoxND<dim>(low,hi,typ);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> bdryHi (const BoxND<dim>& b, int dir, int len=1) noexcept
{
    IntVectND<dim> low(b.smallEnd());
    IntVectND<dim> hi(b.bigEnd());
    auto const bitval = b.type()[dir];
    int bg = hi[dir]  + 1 - bitval%2;
    low.setVal(dir,bg);
    hi.setVal(dir,bg+len-1);
    //
    // Set dir'th bit to 1 = IndexType::NODE.
    //
    IndexTypeND<dim> typ(b.ixType());
    typ.set(dir);
    return BoxND<dim>(low,hi,typ);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> bdryNode (const BoxND<dim>& b, Orientation face, int len=1) noexcept
{
    int dir = face.coordDir();
    IntVectND<dim> low(b.smallEnd());
    IntVectND<dim> hi(b.bigEnd());
    if (face.isLow())
    {
        int sm = low[dir];
        low.setVal(dir,sm-len+1);
        hi.setVal(dir,sm);
    }
    else
    {
        int bitval = b.type()[dir];
        int bg = hi[dir]  + 1 - bitval%2;
        low.setVal(dir,bg);
        hi.setVal(dir,bg+len-1);
    }
    //
    // Set dir'th bit to 1 = IndexType::NODE.
    //
    IndexTypeND<dim> typ(b.ixType());
    typ.set(dir);
    return BoxND<dim>(low,hi,typ);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> adjCellLo (const BoxND<dim>& b, int dir, int len=1) noexcept
{
    BL_ASSERT(len > 0);
    IntVectND<dim> low(b.smallEnd());
    IntVectND<dim> hi(b.bigEnd());
    int sm = low[dir];
    low.setVal(dir,sm - len);
    hi.setVal(dir,sm - 1);
    //
    // Set dir'th bit to 0 = IndexType::CELL.
    //
    IndexTypeND<dim> typ(b.ixType());
    typ.unset(dir);
    return BoxND<dim>(low,hi,typ);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> adjCellHi (const BoxND<dim>& b, int dir, int len=1) noexcept
{
    BL_ASSERT(len > 0);
    IntVectND<dim> low(b.smallEnd());
    IntVectND<dim> hi(b.bigEnd());
    int bitval = b.type()[dir];
    int bg = hi[dir] + 1 - bitval%2;
    low.setVal(dir,bg);
    hi.setVal(dir,bg + len - 1);
    //
    // Set dir'th bit to 0 = IndexType::CELL.
    //
    IndexTypeND<dim> typ(b.ixType());
    typ.unset(dir);
    return BoxND<dim>(low,hi,typ);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> adjCell (const BoxND<dim>& b, Orientation face, int len=1) noexcept
{
    BL_ASSERT(len > 0);
    IntVectND<dim> low(b.smallEnd());
    IntVectND<dim> hi(b.bigEnd());
    int dir = face.coordDir();
    if (face.isLow())
    {
        int sm = low[dir];
        low.setVal(dir,sm - len);
        hi.setVal(dir,sm - 1);
    }
    else
    {
        int bitval = b.type()[dir];
        int bg = hi[dir] + 1 - bitval%2;
        low.setVal(dir,bg);
        hi.setVal(dir,bg + len - 1);
    }
    //
    // Set dir'th bit to 0 = IndexType::CELL.
    //
    IndexTypeND<dim> typ(b.ixType());
    typ.unset(dir);
    return BoxND<dim>(low,hi,typ);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> minBox (const BoxND<dim>& b1, const BoxND<dim>& b2) noexcept
{
    BoxND<dim> result = b1;
    result.minBox(b2);
    return result;
}

namespace detail {
    std::ostream& box_write (std::ostream& os, const int * smallend, const int * bigend,
                             const int * type, int dim);
    std::istream& box_read (std::istream& is, int * smallend, int * bigend, int * type, int dim);
 
    template<std::size_t...Ns, class T, class U>
    AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE constexpr
    auto BoxSplit_imp (std::index_sequence<Ns...>,
                       const T& lo, const T& hi, const U& typ) noexcept {
        return makeTuple(BoxND(get<Ns>(lo), get<Ns>(hi), get<Ns>(typ))...);
    }
}

template<int dim>
std::ostream& operator<< (std::ostream& os, const BoxND<dim>& bx)
{
    IntVectND<dim> type = bx.type();
    return detail::box_write(os, bx.smallEnd().begin(), bx.bigEnd().begin(), type.begin(), dim);
}

template<int dim>
std::istream& operator>> (std::istream& is, BoxND<dim>& bx) {
    IntVectND<dim> small;
    IntVectND<dim> big;
    IntVectND<dim> type;
    detail::box_read(is, small.begin(), big.begin(), type.begin(), dim);
    bx = BoxND<dim>{small, big, type};
    return is;
}

template<int d, int...dims>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
constexpr BoxND<detail::get_sum<d, dims...>()>
BoxCat (const BoxND<d>& bx, const BoxND<dims>&...boxes) noexcept {
    auto lo = IntVectCat(bx.smallEnd(), boxes.smallEnd()...);
    auto hi = IntVectCat(bx.bigEnd(), boxes.bigEnd()...);
    auto typ = IndexTypeCat(bx.ixType(), boxes.ixType()...);
    return BoxND<detail::get_sum<d, dims...>()>{lo, hi, typ};
}

template<int d, int...dims>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
constexpr GpuTuple<BoxND<d>, BoxND<dims>...>
BoxSplit (const BoxND<detail::get_sum<d, dims...>()>& bx) noexcept {
    auto lo = IntVectSplit<d, dims...>(bx.smallEnd());
    auto hi = IntVectSplit<d, dims...>(bx.bigEnd());
    auto typ = IndexTypeSplit<d, dims...>(bx.ixType());
    return detail::BoxSplit_imp(std::make_index_sequence<1 + sizeof...(dims)>(), lo, hi, typ);
}

template<int new_dim, int old_dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
constexpr BoxND<new_dim>
BoxShrink (const BoxND<old_dim>& bx) noexcept {
    return bx.template shrink<new_dim>();
}

template<int new_dim, int old_dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
constexpr BoxND<new_dim>
BoxExpand (const BoxND<old_dim>& bx) noexcept {
    return bx.template expand<new_dim>();
}

template<int new_dim, int old_dim>
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
constexpr BoxND<new_dim>
BoxResize (const BoxND<old_dim>& bx) noexcept {
    return bx.template resize<new_dim>();
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> lbound_iv (BoxND<dim> const& box) noexcept
{
    return box.smallEnd();
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> ubound_iv (BoxND<dim> const& box) noexcept
{
    return box.bigEnd();
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> begin_iv (BoxND<dim> const& box) noexcept
{
    return box.smallEnd();
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> end_iv (BoxND<dim> const& box) noexcept
{
    return box.bigEnd() + 1;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> length_iv (BoxND<dim> const& box) noexcept
{
    return box.bigEnd() - box.smallEnd() + 1;
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> max_lbound_iv (BoxND<dim> const& b1, BoxND<dim> const& b2) noexcept
{
    return max(b1.smallEnd(), b2.smallEnd());
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> max_lbound_iv (BoxND<dim> const& b1, IntVectND<dim> const& lo) noexcept
{
    return max(b1.smallEnd(), lo);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> min_ubound_iv (BoxND<dim> const& b1, BoxND<dim> const& b2) noexcept
{
    return min(b1.bigEnd(), b2.bigEnd());
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> min_ubound_iv (BoxND<dim> const& b1, IntVectND<dim> const& hi) noexcept
{
    return min(b1.bigEnd(), hi);
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 lbound (BoxND<dim> const& box) noexcept
{
    return box.smallEnd().dim3();
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 ubound (BoxND<dim> const& box) noexcept
{
    return box.bigEnd().dim3();
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 begin (BoxND<dim> const& box) noexcept
{
    return box.smallEnd().dim3();
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 end (BoxND<dim> const& box) noexcept
{
    return (box.bigEnd() + 1).dim3(1);
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 length (BoxND<dim> const& box) noexcept
{
    return (box.bigEnd() - box.smallEnd() + 1).dim3(1);
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 max_lbound (BoxND<dim> const& b1, BoxND<dim> const& b2) noexcept
{
    return max(b1.smallEnd(), b2.smallEnd()).dim3();
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 max_lbound (BoxND<dim> const& b1, Dim3 const& lo) noexcept
{
    return max(b1.smallEnd(), IntVectND<dim>(lo)).dim3();
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 min_ubound (BoxND<dim> const& b1, BoxND<dim> const& b2) noexcept
{
    return min(b1.bigEnd(), b2.bigEnd()).dim3();
}

template<int dim>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
Dim3 min_ubound (BoxND<dim> const& b1, Dim3 const& hi) noexcept
{
    return min(b1.bigEnd(), IntVectND<dim>(hi)).dim3();
}
 
template<int dim>
[[nodiscard]]
AMREX_FORCE_INLINE
BoxND<dim> getIndexBounds (BoxND<dim> const& b1) noexcept
{
    return b1;
}

template<int dim>
[[nodiscard]]
AMREX_FORCE_INLINE
BoxND<dim> getIndexBounds (BoxND<dim> const& b1, BoxND<dim> const& b2) noexcept
{
    BoxND<dim> b = b1;
    b.setType(b2.ixType());
    b.minBox(b2);
    return b;
}

template <class T, class ... Ts>
[[nodiscard]]
AMREX_FORCE_INLINE
auto getIndexBounds (T const& b1, T const& b2, Ts const& ... b3) noexcept
{
    return getIndexBounds(getIndexBounds(b1,b2),b3...);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
IntVectND<dim> getCell (BoxND<dim> const* boxes, int nboxes, Long icell) noexcept
{
    int ibox;
    Long ncells_subtotal = 0;
    Long offset = 0;
    for (ibox = 0; ibox < nboxes; ++ibox) {
        const Long n = boxes[ibox].numPts();
        ncells_subtotal += n;
        if (icell < ncells_subtotal) {
            offset = icell - (ncells_subtotal - n);
            break;
        }
    }
    return boxes[ibox].atOffset(offset);
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> makeSlab (BoxND<dim> const& b, int direction, int slab_index) noexcept
{
    BoxND<dim> r = b;
    r.makeSlab(direction,slab_index);
    return r;
}

template<int dim=AMREX_SPACEDIM>
requires ( 1<=dim && dim<=3 )
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> makeSingleCellBox (int i, int j, int k, IndexTypeND<dim> typ = IndexTypeND<dim>::TheCellType())
{
    Dim3 p3d{.x = i, .y = j, .z = k};
    IntVectND<dim> vect{p3d};
    return BoxND<dim>{vect, vect, typ};
}

template<int dim>
[[nodiscard]]
AMREX_GPU_HOST_DEVICE
AMREX_FORCE_INLINE
BoxND<dim> makeSingleCellBox (IntVectND<dim> const& vect, IndexTypeND<dim> typ = IndexTypeND<dim>::TheCellType())
{
    return BoxND<dim>{vect, vect, typ};
}

template<int dim>
struct BoxIndexerND
{
    std::uint64_t npts;
    Math::FastDivmodU64 fdm[dim-1];
    IntVectND<dim> lo;
 
    BoxIndexerND (BoxND<dim> const& box)
        : npts(box.numPts()),
          lo  (box.smallEnd())
        {
            std::uint64_t mult = 1;
            for (int i=0; i<dim-1; ++i) {
                mult *= box.length(i);
                fdm[i] = Math::FastDivmodU64(mult);
            }
        }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    IntVectND<dim> intVect (std::uint64_t icell) const
    {
        IntVectND<dim> retval = lo;
 
        for (int i=dim-1; i>0; --i) {
            std::uint64_t quotient, remainder;
            fdm[i-1](quotient, remainder, icell);
            retval[i] += quotient;
            icell = remainder;
        }
 
        retval[0] += icell;
 
        return retval;
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    Dim3 operator()(std::uint64_t icell) const
        requires (1 <= dim && dim <= 3)
    {
        return intVect(icell).dim3();
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    std::uint64_t numPts () const { return npts; }
};

template<>
struct BoxIndexerND<1>
{
    std::uint64_t npts;
 
    IntVectND<1> lo;

    BoxIndexerND (BoxND<1> const& box)
        : npts(box.numPts()),
          lo(box.smallEnd(0))
        {}

    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    IntVectND<1> intVect (std::uint64_t icell) const
    {
        return IntVectND<1>{int(icell)+lo[0]};
    }
 
    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    Dim3 operator() (std::uint64_t icell) const
    {
        return Dim3{.x = int(icell)+lo[0], .y = 0, .z = 0};
    }

    [[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
    std::uint64_t numPts () const { return npts; }
};
 
using BoxIndexer = BoxIndexerND<AMREX_SPACEDIM>;

namespace detail {
// The points of bx whose index equals offset modulo stride: lower corner is
// the first such point, lengths are the numbers of such points.
[[nodiscard]] AMREX_GPU_HOST_DEVICE AMREX_FORCE_INLINE
Box strided_box (Box const& bx, IntVect const& stride, IntVect const& offset)
{
    IntVect lo, hi;
    for (int d = 0; d < AMREX_SPACEDIM; ++d) {
        const int s = stride[d];
        lo[d] = bx.smallEnd(d) + ((offset[d]-bx.smallEnd(d))%s + s) % s;
        hi[d] = lo[d] + (bx.bigEnd(d)-lo[d]+s)/s - 1;
    }
    return Box(lo, hi);
}
}
 
}
 
#endif /*AMREX_BOX_H*/