pow calculation in kernel

Hi: I am doing a research on D2TCP(http://dl.acm.org/citation.cfm?id=2342388), I just want to implement it into the linux kernel. When calculating the penalty function, it is p = a^d, where 0< a < 1 and 0< d < 1. Since the kernel only offers integer, so in my code, so I let a multiply 2^10. But I have no idea of calculating a^d when 0< d < 1. May be I want a approximate algorithm or other methods. Can you help me ? thanks~ ------------------ 祝好， 张晗 ---------- HanZhang School of Computer Science Tsinghua University, Beijing, 100084, P.R.CHINA Mobile: +86 156-526-59782 E-mail: zhanghan@csnet1.cs.tsinghua.edu.cn