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  1. #include <cmath>
  2. #include <iostream>
  3. #include <iomanip>
  4. #include <limits>
  5. #include <sstream>
  6.  
  7. std::string make_string(double x, int precision)
  8. {
  9. 	std::ostringstream output;
  10. 	output << std::setprecision(precision) << x;
  11. 	return output.str();
  12. }
  13.  
  14. int digits_before_point(double x)
  15. {
  16. 	return x ? int(floor(std::log(std::abs(x)) / std::log(10.0) + 1)) : 0;
  17. }
  18.  
  19. std::string format(double x, int precision = 2)
  20. {
  21. 	const auto dbp = digits_before_point(x);
  22. 	if (dbp + precision > 0)
  23. 	{
  24. 		return make_string(x, dbp + precision);
  25. 	}
  26. 	else if (dbp + precision == 0)
  27. 	{
  28. 		const double min_value = std::exp(-precision * std::log(10));
  29. 		if (x >= min_value / 2)
  30. 		{
  31. 			return make_string(min_value, 1);
  32. 		}
  33. 		else if(x <= -min_value / 2)
  34. 		{
  35. 			return make_string(-min_value, 1);
  36. 		}
  37. 	}
  38. 	return "0";
  39. }
  40.  
  41. int main()
  42. {
  43. 	std::cout << format(0x1.6bcc41e8ffffap+46) << std::endl;
  44. }
Success #stdin #stdout 0s 4380KB
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99999999999999.906
https://ideone.com/msG3Jo
language:
C++14 (clang 8.0)
created:
4 years ago
visibility:
public

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