## This a modified version of the example provided in the Rcpp package
## from Dirk Eddelbuettel and Romain Francois
## in response to the "Julia, I love you" post at:
## http://www.johnmyleswhite.com/notebook/2012/03/31/julia-i-love-you/

require(inline)
require(compiler)

## Rcpp version
incltxt <- '
int fibonacci(const int x) {
   if (x == 0) return(0);
   if (x == 1) return(1);
   return (fibonacci(x - 1)) + fibonacci(x - 2);
}'

## now use the snipped above as well as one argument conversion
## in as well as out to provide Fibonacci numbers via C++
fibRcpp <- cxxfunction(signature(xs="int"),
                       plugin="Rcpp",
                       incl=incltxt,
                       body='
   int x = Rcpp::as<int>(xs);
   return Rcpp::wrap( fibonacci(x) );
')

# David J. Harris
fib2 <- function(n){
  if(n < 2){n}
  else{fib2(n – 1) + fib2(n – 2)}
}

# G. Grothendieck
fib2a <- function(n) {
  if (n < 3) 1
  else {
    y <- rep(1, n)
    for(i in 3:n) y[i] <- {y[i-1] + y[i-2]}
    y[n]
  }
}

library(compiler)
fib2c <- compiler(fib2a)

## load rbenchmark to compare
library(rbenchmark)

N <- 25
res <- benchmark(fibRcpp(N),
                 fib2(N),
                 fib2a(N),
                 fib2c(N),
                 columns=c("test", "replications", "elapsed",
                          "relative"),
                 order="relative",
                 replications=20)
print(res)  ## show result