module BSON::Decimal128::Builder

def parts_to_bits(significand, exponent, is_negative)
  validate_range!(exponent, significand)
  exponent = exponent + Decimal128::EXPONENT_OFFSET
  high = significand >> 64
  low = (high << 64) ^ significand
  if high >> 49 == 1
    high = high & 0x7fffffffffff
    high |= TWO_HIGHEST_BITS_SET
    high |= (exponent & 0x3fff) << 47
  else
    high |= exponent << 49
  end
  if is_negative
    high |= SIGN_BIT_MASK
  end
  [ low, high ]
end

def valid_exponent?(exponent)
  exponent <= Decimal128::MAX_EXPONENT && exponent >= Decimal128::MIN_EXPONENT
end

def valid_significand?(significand)
  significand.to_s.length <= Decimal128::MAX_DIGITS_OF_PRECISION
end

def validate_range!(exponent, significand)
  unless valid_exponent?(exponent)
    raise Error::InvalidDecimal128Range.new
  end
  unless valid_significand?(significand)
    raise Error::UnrepresentablePrecision.new
  end
end