包含求反余弦函数,计算Y/X的反正切值 ,向上舍入,把一个双精度数分解为尾数的指数,计算直角三角形的斜边长-include cosine function for calculating Y/X arc tangent, rounded upward, a few double precision decomposition of the final index, calculated length of the hypotenuse of the right triangle, etc.