4 kinds of factorial

factorials.rb

require "benchmark/ips"

def recursive_factorial(n)
  n < 2 ? 1 : n * recursive_factorial(n - 1)
end

def tail_recursive_factorial(n, accumulator = 1)
  n < 2 ? accumulator : tail_recursive_factorial(n - 1, n * accumulator)
end

code = <<-CODE
  def tco_factorial(n, accumulator = 1)
    n < 2 ? accumulator : tco_factorial(n - 1, n * accumulator)
  end
CODE
RubyVM::InstructionSequence.new(code, nil, nil, nil, {
  tailcall_optimization: true,
  trace_instruction: false,
}).eval

def loopy_factorial(n)
  return 1 if n < 2
  accumulator = 1
  while n > 1
    accumulator *= n
    n -= 1
  end
  accumulator
end

i = 15
Benchmark.ips do |bm|
  bm.report("recursive_factorial") do
    recursive_factorial(i)
  end

  bm.report("tail_recursive_factorial") do
    tail_recursive_factorial(i)
  end

  bm.report("tco_factorial") do
    tco_factorial(i)
  end

  bm.report("loopy_factorial") do
    loopy_factorial(i)
  end
end