问如何在R代码中调用核心C函数？

EN

Error in hw(alpha, beta, gamma) : object 'C_HoltWinters' not found

 hw <- function(alpha, beta, gamma)
        .C(C_HoltWinters,
           as.double(x),
           lenx,
           as.double(max(min(alpha, 1), 0)),
           as.double(max(min(beta, 1), 0)),
           as.double(max(min(gamma, 1), 0)),
           as.integer(start.time),
           ## no idea why this is so: same as seasonal != "multiplicative"
           as.integer(! + (seasonal == "multiplicative")),
           as.integer(f),
           as.integer(!is.logical(beta) || beta),
           as.integer(!is.logical(gamma) || gamma),

           a = as.double(l.start),
           b = as.double(b.start),
           s = as.double(s.start),

       ## return values
           SSE = as.double(0),
           level = double(len + 1L),
           trend = double(len + 1L),
           seasonal = double(len + f)
           )

1) How can I find out `dll` name for this function? 
2) If I run default `HoltWinters.R` we don't need to load `dll`, then why it is required load `dll` in my custom script case?