rthconv <- function(x,y) {
   dyn.load("rthconv.so")
   nx <- length(x)
   ny <- length(y)
   tmp <- .C("rthconv",as.double(x),as.integer(nx),as.double(y),as.integer(ny),
      tmpres=double(nx+ny-1))
   return(tmp$tmpres)
}