Ruby 2.3での階乗計算

output.txt

Warming up --------------------------------------
                  **    70.304k i/100ms
              my pow    27.298k i/100ms
Calculating -------------------------------------
                  **      1.633M (± 5.7%) i/s -      8.155M in   5.012777s
              my pow    345.490k (± 3.6%) i/s -      1.747M in   5.063730s

Comparison:
                  **:  1632697.1 i/s
              my pow:   345489.6 i/s - 4.73x  slower

"2.3.8"
true

pow.rb

require 'benchmark/ips'

def my_pow(i, n)
  return 1 if n == 0
  x = my_pow(i, n / 2)
  x = x * x
  if (n % 2 == 1)
    x = x * 2
  end
  return x
end

n = 10 * 9 + 7

Benchmark.ips do |x|
  x.report("**") do
    2 ** n
  end

  x.report('my pow') do
    my_pow(2, n)
  end

  x.compare!
end

p RUBY_VERSION
p 2 ** n == my_pow(2, n)