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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. double power(double x, int n)
  5. {
  6.   // key is to avoid re-calculating something you’ve done.
  7.   if(n==0)
  8.      return double(1);
  9.   else if(n<0)
  10.   	 return 1/power(x, -n);
  11.   else
  12.   {
  13.     double pow2s[sizeof(int)*8];
  14.     pow2s[0] = x;
  15.     double result = 1;
  16.     int bit = 0;
  17.     while(true)
  18.     {
  19.        if(n&0x1)
  20.          result *= pow2s[bit];
  21.        n >>= 1;
  22.        if(0==n)
  23.          break;
  24.        pow2s[bit+1] = pow2s[bit] * pow2s[bit];
  25.        ++bit;
  26.     }
  27.     return result;
  28.   }
  29. }
  30.  
  31.  
  32. int main() {
  33. 	std::cout << power(2.0, 0) << std::endl;
  34. 	std::cout << power(2.0, 1) << std::endl;
  35. 	std::cout << power(2.0, 3) << std::endl;
  36. 	std::cout << power(2.0, 5) << std::endl;
  37. 	std::cout << power(2.0, -4) << std::endl;
  38.  
  39. 	return 0;
  40. }
Success #stdin #stdout 0s 3140KB
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0.0625
https://ideone.com/D00Mc3
language:
C++ (gcc 8.3)
created:
8 years ago
visibility:
public

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