[计] two-word integer support routine

shuāng zì zhěng shù zhī yuán chéng xù ㄕㄨㄤ ㄗˋ ㄓㄥˇ ㄕㄨˋ ㄓ ㄩㄢˊ ㄔㄥˊ ㄒㄩˋ