Get negative-base number from an integer

negative_base.rb

# Returns an array which index [0] represents the least significant bit. 
# to_negativebase(9)   # => [1, 0, 0, 1, 1]
# to_negativebase(-9)  # => [1, 1, 0, 1]
def to_negativebase(value, base = -2)
  raise ArgumentError if base > -2
  digits = []
  while value != 0
    value, mod = value.divmod(base)
    if mod < 0
      mod += -base
      value += 1
    end
    digits << mod
  end
  digits
end

# Converts a r-based number to an integer.
# The array[0] represents the least significant bit.
def to_int(a, base = -2)
  a.each_with_index.inject(0) { |result, (n, i)| result + n * (base ** i) }
end