/*************************************************************************
 * Copyright (c) 2015-2022, NVIDIA CORPORATION. All rights reserved.
 *
 * See LICENSE.txt for license information
 ************************************************************************/

#include "device.h"
#include "collectives.h"
#include "primitives.h"

namespace {
  template<typename T, typename RedOp, typename Proto>
  __device__ __forceinline__ void runRing(int tid, int nthreads, struct ncclDevWorkColl* work) {
    ncclRing *ring = &ncclShmem.channel.ring;
    const int nranks = ncclShmem.comm.nRanks;
    const int rank = ncclShmem.comm.rank;
    const int prevRank = ring->userRanks[nranks-1];
    const int root = work->root;
    size_t chunkCount;
    size_t channelCount;
    size_t gridOffset;
    ncclCollCbdPart(work, ncclShmem.channelId, Proto::Id, sizeof(T), (size_t*)nullptr, &gridOffset, &channelCount, &chunkCount);
    size_t offset;
    int nelem;

    // Coverity reports that the callee treats &ring->next as an array.  However, due to the use of
    // FanSymmetric<1>, only the first element is ever accessed, so it's fine.
    // coverity[callee_ptr_arith:FALSE]
    Primitives<T, RedOp, FanSymmetric<1>, 0, Proto, 0>
      prims(tid, nthreads, &ring->prev, &ring->next, work->sendbuff, work->recvbuff, work->redOpArg);

    if (prevRank == root) {
      for (size_t elemOffset = 0; elemOffset < channelCount; elemOffset += chunkCount) {
        offset = gridOffset + elemOffset;
        nelem = min(chunkCount, channelCount - elemOffset);
        prims.send(offset, nelem);
      }
    }
    else if (rank == root) {
      for (size_t elemOffset = 0; elemOffset < channelCount; elemOffset += chunkCount) {
        offset = gridOffset + elemOffset;
        nelem = min(chunkCount, channelCount - elemOffset);
        prims.recvReduceCopy(offset, offset, nelem, /*postOp=*/true);
      }
    }
    else {
      for (size_t elemOffset = 0; elemOffset < channelCount; elemOffset += chunkCount) {
        offset = gridOffset + elemOffset;
        nelem = min(chunkCount, channelCount - elemOffset);
        prims.recvReduceSend(offset, nelem);
      }
    }
  }
}

template<typename T, typename RedOp>
struct RunWorkColl<ncclFuncReduce, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_SIMPLE> {
  __device__ __forceinline__ void run(int tid, int nthreads, struct ncclDevWorkColl* work) {
    using Proto = ProtoSimple<REDUCE_CHUNKSTEPS/REDUCE_SLICESTEPS, REDUCE_SLICESTEPS>;
    runRing<T, RedOp, Proto>(tid, nthreads, work);
  }
};

template<typename T, typename RedOp>
struct RunWorkColl<ncclFuncReduce, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_LL> {
  __device__ __forceinline__ void run(int tid, int nthreads, struct ncclDevWorkColl* work) {
    runRing<T, RedOp, ProtoLL>(tid, nthreads, work);
  }
};

template<typename T, typename RedOp>
struct RunWorkColl<ncclFuncReduce, T, RedOp, NCCL_ALGO_RING, NCCL_PROTO_LL128> {
  __device__ __forceinline__ void run(int tid, int nthreads, struct ncclDevWorkColl* work) {
    runRing<T, RedOp, ProtoLL128>(tid, nthreads, work);
  }
};