ceil 方法上有这么一段注释：If the argument value is less than zero but greater than -1.0, then the result is negative zero
如果参数小于0且大于-1.0，结果为 -0
1
Math.floor(d1)
ceil 和 floor 方法 上都有一句话：If the argument is NaN or an infinity or positive zero or negative zero, then the result is the same as the argument，意思为：如果参数是 NaN、无穷、正 0、负 0，那么结果与参数相同，
