Function cusparseSpGEMM_estimateMemory 

pub unsafe extern "C" fn cusparseSpGEMM_estimateMemory(
    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,
    chunk_fraction: f32,
    bufferSize3: *mut size_t,
    externalBuffer3: *mut c_void,
    bufferSize2: *mut size_t,
) -> cusparseStatus_t