example.rb

def fib(n)
  return n if 1 >= n
  fib(n-1) + fib(n-2) if n > 1
end

def fib_include(n)
  return n if (0..1).include? n
  fib_include(n-1) + fib_include(n-2) if n > 1
end

require 'benchmark'

n = ARGV[0].to_i
Benchmark.bm(8) do |x|
  x.report("1 >= n")  { fib n }
  x.report("include") { fib_include n }
end