cuda_toolkit/include/cooperative_groups/details/partitioning.h

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#ifndef _CG_PARTITIONING_H
#define _CG_PARTITIONING_H

#include "info.h"
#include "helpers.h"

_CG_BEGIN_NAMESPACE

namespace details {

    template <typename TyGroup>
    _CG_STATIC_QUALIFIER coalesced_group _binary_partition(const TyGroup &tile, bool pred) {
        const unsigned int fullMask = ~0u;

        unsigned int thisMask = _coalesced_group_data_access::get_mask(tile);
        unsigned int predMask = pred ? 0 : fullMask;
        unsigned int setMask = __ballot_sync(thisMask, pred);

        if (setMask == thisMask || setMask == 0) {
            coalesced_group subTile = _coalesced_group_data_access::construct_from_mask<coalesced_group>(thisMask);
            _coalesced_group_data_access::modify_meta_group(subTile, 0, 1);
            return subTile;
        }
        else {
            unsigned int subMask = thisMask & (setMask ^ predMask);
            coalesced_group subTile = _coalesced_group_data_access::construct_from_mask<coalesced_group>(subMask);
            _coalesced_group_data_access::modify_meta_group(subTile, pred, 2);
            return subTile;
        }
    }

#if defined(_CG_HAS_MATCH_COLLECTIVE) && defined(_CG_CPP11_FEATURES)
    template <typename TyPredicate>
    struct _labeled_partition_dispatch {
        template <typename TyGroup>
        _CG_QUALIFIER coalesced_group operator()(const TyGroup &tile, TyPredicate pred) {
            unsigned int thisMask = _coalesced_group_data_access::get_mask(tile);
            unsigned int thisBias = __ffs(thisMask) - 1; // Subtract 1 to index properly from [1-32]
            unsigned int subMask = __match_any_sync(thisMask, pred);

            coalesced_group subTile = _coalesced_group_data_access::construct_from_mask<coalesced_group>(subMask);

            int leaderLaneId = subTile.shfl(details::laneid(), 0);

            bool isLeader = !subTile.thread_rank();
            unsigned int leaderMask = __ballot_sync(thisMask, isLeader);
            unsigned int tileRank = __fns(leaderMask, leaderLaneId, 0) - thisBias;

            _coalesced_group_data_access::modify_meta_group(subTile, tileRank, __popc(leaderMask));

            return subTile;
        }
    };

    template <>
    struct _labeled_partition_dispatch<bool> {
        template <typename TyGroup>
        _CG_QUALIFIER coalesced_group operator()(const TyGroup &tile, bool pred) {
            return _binary_partition(tile, pred);
        }
    };

    template <typename TyPredicate>
    struct _labeled_partition_dispatch<TyPredicate*> {
        template <typename TyGroup>
        _CG_QUALIFIER coalesced_group operator()(const TyGroup &tile, TyPredicate* pred) {
            auto impl = _labeled_partition_dispatch<unsigned long long>();
            return impl(tile, reinterpret_cast<unsigned long long>(pred));
        }
    };
#endif
}; // namespace details

_CG_STATIC_QUALIFIER coalesced_group binary_partition(const coalesced_group &tile, bool pred) {
    return details::_binary_partition(tile, pred);
}

template <unsigned int Size, typename ParentT>
_CG_STATIC_QUALIFIER coalesced_group binary_partition(const thread_block_tile<Size, ParentT> &tile, bool pred) {
#ifdef _CG_CPP11_FEATURES
    static_assert(Size <= 32, "Binary partition is available only for tiles of size smaller or equal to 32");
#endif
    return details::_binary_partition(tile, pred);
}


#if defined(_CG_HAS_MATCH_COLLECTIVE) && defined(_CG_CPP11_FEATURES)
template <typename TyPredicate>
_CG_STATIC_QUALIFIER coalesced_group labeled_partition(const coalesced_group &tile, TyPredicate pred) {
    static_assert(_CG_STL_NAMESPACE::is_integral<TyPredicate>::value ||
                  _CG_STL_NAMESPACE::is_pointer<TyPredicate>::value,
                  "labeled_partition predicate must be an integral or pointer type");
    auto dispatch = details::_labeled_partition_dispatch<details::remove_qual<TyPredicate>>();
    return dispatch(tile, pred);
}

template <typename TyPredicate, unsigned int Size, typename ParentT>
_CG_STATIC_QUALIFIER coalesced_group labeled_partition(const thread_block_tile<Size, ParentT> &tile, TyPredicate pred) {
    static_assert(_CG_STL_NAMESPACE::is_integral<TyPredicate>::value ||
                  _CG_STL_NAMESPACE::is_pointer<TyPredicate>::value,
                  "labeled_partition predicate must be an integral or pointer type");
    static_assert(Size <= 32, "Labeled partition is available only for tiles of size smaller or equal to 32");
    auto dispatch = details::_labeled_partition_dispatch<details::remove_qual<TyPredicate>>();
    return dispatch(tile, pred);
}
#endif

_CG_END_NAMESPACE

#endif // _CG_PARTITIONING_H