fib.ex

defmodule Standard do
  def fib(0), do: 0
  def fib(1), do: 1
  def fib(n), do: fib(n-1) + fib(n-2)
end

defmodule Optimized do
  def fib(0), do: 0
  def fib(1), do: 1
  def fib(1, current, _), do: current
  def fib(n, current \\ 1, previous \\ 0) do
    fib(n - 1, current + previous, current)
  end
end

defmodule Matrix do
  def fib(n) do
    eigen1 = (1 + :math.sqrt(5))/2
    eigen2 = (1 - :math.sqrt(5))/2
    ((1 / :math.sqrt(5)) * (:math.pow(eigen1, n) - :math.pow(eigen2, n)))
  end
end

:eprof.start
:eprof.start_profiling([self])
Standard.fib(20)
Optimized.fib(20)
Matrix.fib(20)
:eprof.stop_profiling()
:eprof.analyze()

# ****** Process <0.48.0>    -- 100.00 % of profiled time ***
# FUNCTION                  CALLS      %  TIME  [uS / CALLS]
# --------                  -----    ---  ----  [----------]
# 'Elixir.Matrix':fib/1         1   0.03     1  [      1.00]
# 'Elixir.Optimized':fib/3     20   0.05     2  [      0.10]
# 'Elixir.Standard':fib/1   21891  99.34  3636  [      0.17]

fib.js

function fib(n) {
    return n <= 2 ? 1 : fib(n-2) + fib(n-1);
}

fib.m

- (NSUInteger)fib:(NSUInteger)n {
    if (n < 2) {
      return 1;
    }
    return [self fib:(n - 1)] + [self fib:(n - 2)];
}

fib.php

function fib($n) {
  if ($n <= 2) {
    return 1;
  }
  return fib($n - 2) + fib($n - 1);
}

fib.rb

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

fib.swift

func fib(n: Int) -> Int {
    return n <= 2 ? 1 : fib(n - 2) + fib(n - 1)
}

fib(10)