Binary euclidean recursive algorithm for gcd

find_gcd.rb

def find_gcd(a, b)
  if a == 0; b
  elsif b == 0; a
  elsif a == b; a
  elsif a == 1 || b == 1; 1
  elsif a.even? && b.even?; 2 * find_gcd(a / 2, b / 2)
  elsif a.even? && b.odd?; find_gcd(a / 2, b)
  elsif a.odd?  && b.even?; find_gcd(a, b / 2)
  elsif a.odd?  && b.odd?; (b > a) ? find_gcd((b - a) / 2, a) : find_gcd((a - b) / 2, b)
  end
end