[R] stepping into a .C call

[Fred J.]

Hello
The Debug and mvbutils packages by Mark Bravington
have been a great help for me in learning R, until I
come to a line in the R code like ".C("fun name",...).
Is there a way to step into this call and see what the
source code does exactly to the supplied arrgs? 
One example in the "fdim" package, a line like 
DK <- .C("pointdif", as.integer(NumRow),
as.integer(NumCol), as.integer(X), NumpDif =
as.integer(NumpDif))
I would like to know what the code does inorder to
come up with the value to assign to DK.

Thanks