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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. template<size_t N, typename T>
  5. size_t bitcount(T v, enable_if_t<(N <= 1)>* = 0)
  6. {
  7. 	static const unsigned char BitsSetTable256[256] = 
  8. 	{
  9. #		define B2(n) n,     n+1,     n+1,     n+2
  10. #		define B4(n) B2(n), B2(n+1), B2(n+1), B2(n+2)
  11. #		define B6(n) B4(n), B4(n+1), B4(n+1), B4(n+2)
  12. 		B6(0), B6(1), B6(1), B6(2)
  13. 	};
  14. 	return BitsSetTable256[v & 0xff];
  15. }
  16.  
  17. template<size_t N, typename T>
  18. size_t bitcount(T v, enable_if_t<(N > 1)>* = 0)
  19. {
  20. 	return bitcount<1>(v) + bitcount<N - 1>(v >> 8);
  21. }
  22.  
  23. int main() {
  24. 	// your code goes here
  25. 	cout << bitcount<4>(0x01234567) << endl;
  26. 	cout << bitcount<8>(0x0123456789abcdefULL) << endl;
  27. 	return 0;
  28. }
Success #stdin #stdout 0s 3412KB
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https://ideone.com/8Yp3YQ
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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