digits memo

integerdigits.rb

class Integer
  alias_method :original_digits, :digits
  def digits(base)
    bits = bit_length
    base_bits = base.bit_length
    return original_digits base if bits < base_bits * 64 # return [self] if self < base
    if base == 1 << (base_bits - 1)
      n = base_bits - 1
      # return Array.new((bits + n - 1) / n) { self[n * _1, n] } # but it's slow
      return Array.new((bits + n - 1) / n) { |i| k = 0; j = 0; while j < n; k |= self[n * i + j] << j; j += 1; end; k }
    end
    arr = digits(base ** 2).flat_map { [_1 % base, _1 / base] }
    arr.pop if arr.last.zero?
    arr
  end

  def digits2
    return bit_length.times.map { |i| self[i] }
  end
end