数值的整数次方

题目：

实现函数double Power(double base, int exponent)，求base的exponent次方。不得使用库函数，同时不需要考虑大数问题。

解答：

public class Solution {
    public static void main(String[] args) {
        double base = 2.1;
        int exponent = 2;
        System.out.println(power(base, exponent));
    }

    public static double power(double base, int exponent) {
        if(equal(base, 0.0) && exponent < 0) {
            return 0.0;
        }

        // 指数的绝对值
        int absExponent = Math.abs(exponent);
        double result = powerWithExponent(base, absExponent);

        if(exponent < 0) {
            result = 1.0 / result;
        }

        return result;
    }


    private static double powerWithExponent(double base, int exponent) {
        if(exponent == 0) {
            return 1.0;
        }

        if(exponent == 1) {
            return base;
        }

        double result = powerWithExponent(base, exponent>>1);
        result = result*result;
        if(exponent & 0x01 == 1) {
            result = result*base;
        }

        return result;
    }

    // important here
    private static boolean equal(double num1, double num2) {
        if((num1 - num2) > -0.0000001 && (num1 - num2) < 0.0000001) {
            return true;
        } else {
            return false;
        }
    }
}