(PHP 5, PHP 7 >= 5.6.0)
gmp_root — Take the integer part of nth root
Takes the nth root of a and
returns the integer component of the result.
a可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。
nth
The positive root to take of a.
The integer component of the resultant root, as a GMP number.