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快速乘方

a= an/2*an/2   , n为even

a= a(n-1)/2*a(n-1)/2 *a  , n为odd

 

double powerWithUnsignedExponent(double base, unsigned int exponent){      if(0 == exponent)          return 1;      if(1 == exponent)          return base;      double result = powerWithUnsignedExponent(base, exponnet >> 1);          result *= result;      if(1 == exponent & 0x1)     //二进制末尾为1,一定是奇数          result *= base;       return result;}

 

借助位运算判断奇偶性:

a & 0x1 == 0;    //even偶数

a & 0x1 != 0;     //odd奇数

 

快速乘方