Function cusparseSpGEMM_workEstimation 

pub unsafe extern "C" fn cusparseSpGEMM_workEstimation(
    handle: cusparseHandle_t,
    opA: cusparseOperation_t,
    opB: cusparseOperation_t,
    alpha: *const c_void,
    matA: cusparseConstSpMatDescr_t,
    matB: cusparseConstSpMatDescr_t,
    beta: *const c_void,
    matC: cusparseSpMatDescr_t,
    computeType: cudaDataType,
    alg: cusparseSpGEMMAlg_t,
    spgemmDescr: cusparseSpGEMMDescr_t,
    bufferSize1: *mut size_t,
    externalBuffer1: *mut c_void,
) -> cusparseStatus_t