任意数的整数次方

/**
 * Created by wuchao on 17-3-29.
 */
import java.util.*;
public class test {
    public static int array[] = {1,1,0,1,1,1,1};
    public static void main(String[] args) {
        System.out.println(power(2,-3));
    }
    public static double power(double base,int exponent){
        //首先判断base是否为0,但double不能直接和0比较
        if(base<0.0000001 && base>-0.0000001) return 0;
        if(exponent==0) return 1;
        int flag=1;//正负标志
        if(exponent<0) {
            flag=-1;
            exponent=-exponent;
        }
        double result = powerWithunsigned(base,exponent);
        if(flag>0) return result;
        return 1/result;
    }
    //exponent>0
    public static double powerWithunsigned(double base,int exponent){
        if(exponent==0) return 1;
        if(exponent==1) return base;
        double result = powerWithunsigned(base,exponent>>1);
        result = result*result;
        //如果exponent为奇数
        if((exponent&1)>0){
            result=result*base;
        }
        return result;
    }
}