Four bit adder

# title: Four bit adder
# source: https://rosettacode.org/wiki/Four_bit_adder
# category: Rosetta Code
# difficulty: Easy
# summary: Add two four-bit binary values and return the carry with the result bits.
# tags: popular, bits, arithmetic, arrays
# vibe: 0.2

def add_four_bits(left, right)
  carry = 0
  result = []
  index = 3

  while index >= 0
    total = left[index] + right[index] + carry
    result = [total % 2] + result

    if total >= 2
      carry = 1
    else
      carry = 0
    end

    index = index - 1
  end

  {
    carry: carry,
    bits: result
  }
end

def run
  {
    five_plus_six: add_four_bits([0, 1, 0, 1], [0, 1, 1, 0]),
    fifteen_plus_one: add_four_bits([1, 1, 1, 1], [0, 0, 0, 1])
  }
end