How to calculate confidence interval for count data in R?

exactPoiCI <- function (X, conf.level=0.95) {
  alpha = 1 - conf.level
  upper <- 0.5 * qchisq(1-alpha/2, 2*X+2)
  lower <- 0.5 * qchisq(alpha/2, 2*X)
  return(c(lower, upper))
}

exactPoiCI(42, 0.9)
exactPoiCI(42)
exactPoiCI(42, 0.99)