crystal-big-int.cr

require "big_int"

struct BigInt2 < Int
  def initialize(num : Int::Signed)
    if LibC::Long::MIN <= num <= LibC::Long::MAX
      LibGMP.init_set_si(out @mpz, num)
    else
      LibGMP.init_set_str(out @mpz, num.to_s, 10)
    end
  end

  def +(other : BigInt2)
    LibGMP.add(mpz, self, other)
    self
  end

  def to_s
    String.new(to_cstr)
  end

  def to_s(io)
    str = to_cstr
    io.write Slice.new(str, LibC.strlen(str))
  end

  private def mpz
    pointerof(@mpz)
  end

  private def to_cstr
    LibGMP.get_str(nil, 10, mpz)
  end

  def to_unsafe
    mpz
  end
end

def fibonacci(n)
  a, b = BigInt.new(0), BigInt.new(1)
  n.times { a, b = b, a + b }
  a
end
start = Time.now
fib = fibonacci 500_000
puts Time.now - start

def fibonacci2(n)
  a, b = BigInt2.new(0), BigInt2.new(1)
  n.times { a, b = b, a + b }
  a
end
start = Time.now
fib2 = fibonacci2 500_000
puts Time.now - start

puts fib.to_s == fib2.to_s