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  1. #include <iostream>
  2. #include <chrono>
  3. #include <cstdint>
  4. #include <cmath>
  5. #include <ratio>
  6. using namespace std;
  7.  
  8. float InvSqrt(float x){
  9.     float xhalf = 0.5f * x;
  10.     int i = *(int*)&x;            // store floating-point bits in integer
  11.     i = 0x5f3759df - (i >> 1);    // initial guess for Newton's method
  12.     x = *(float*)&i;              // convert new bits into float
  13.     x = x*(1.5f - xhalf*x*x);     // One round of Newton's method
  14.     return x;
  15. }
  16.  
  17. int main() {
  18. 	const int32_t SampleSize = 1000000;
  19. 	int64_t Resolution = std::chrono::high_resolution_clock::period::den;
  20. 	std::cout << "Resolution: " << Resolution << std::endl;
  21. 	float Sum = 0.0f;
  22. 	auto Begin = std::chrono::high_resolution_clock::now();
  23. 	for(int32_t i=1;i<SampleSize;i++){
  24. 			Sum+=1.0f/sqrtf((float)i);
  25. 	}
  26. 	auto End = std::chrono::high_resolution_clock::now();
  27. 	std::cout << "Time Taken for 1/sqrt(i): " << (std::chrono::duration_cast<std::chrono::duration<double>>(End-Begin)).count() << " seconds. Total Sum: "  << Sum << std::endl;
  28. 	Sum = 0.0f;
  29. 	Begin = std::chrono::high_resolution_clock::now();
  30. 	for(int32_t i=1;i<SampleSize;i++){
  31. 		Sum+=InvSqrt((float)i);
  32. 	}
  33. 	End = std::chrono::high_resolution_clock::now();
  34. 	std::cout << "Time Taken for InvSqrt(i): " << (std::chrono::duration_cast<std::chrono::duration<double>>(End-Begin)).count() << " seconds. Total Sum: "  << Sum << std::endl;
  35.  
  36. 	// your code goes here
  37. 	return 0;
  38. }
Success #stdin #stdout 0.03s 3096KB
comments (?)
stdin 
Standard input is empty
stdout 
Resolution: 1000000000
Time Taken for 1/sqrt(i): 0.0247454 seconds. Total Sum: 1998.54
Time Taken for InvSqrt(i): 0.00630476 seconds. Total Sum: 1996.65
https://ideone.com/6iUX2P
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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