use prefixSum instead of reduction

    int smaller = 0, bigger = 0;

    cmpElem(arr, myBegin, myEnd, pivot, smaller, bigger);

    int smallerOffset = blockReduceSum(smaller);

    int biggerOffset = blockReduceSum(bigger);

    int smallerOffset = blockPrefixSum(smaller);

    int biggerOffset = blockPrefixSum(bigger);

    if (threadIdx.x == 0)

    if (threadIdx.x == blockDim.x - 1)

    {

        *smallerStart = atomicAdd(auxBeginIdx, smallerOffset);

        *biggerStart = atomicAdd(auxEndIdx, -biggerOffset) - biggerOffset;

    }

    __syncthreads();

    int auxThreadSmallerBegin = atomicAdd(smallerStart, smaller);

    int auxThreadBiggerBegin = atomicAdd(biggerStart, bigger);

    copyData(arr, myBegin, myEnd, pivot, aux, auxThreadSmallerBegin, auxThreadBiggerBegin);

    copyData(arr, myBegin, myEnd, pivot, aux, (*smallerStart) + smallerOffset - smaller, (*biggerStart) + biggerOffset - bigger);

    __syncthreads();

    //inserts pivot