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  1. #include <cmath>
  2. #include <iostream>
  3. #include <iomanip>
  4. #include <limits>
  5.  
  6. using namespace std;
  7.  
  8. void f(const uint64_t n) {
  9.   const auto d = static_cast<double>(n);
  10.   const long double ld = n;
  11.  
  12.   cout << "Original:          " << n << endl << setprecision(50);
  13.  
  14.   if(ld == d) {
  15.   	cout << "Lower bound:       " << d << "\nUpper bound:       " << d << "\nPrecision loss:    " << 0.0 << "\n\n";
  16.   } else if(ld < d) {
  17.     const double f = nextafter(d, -numeric_limits<double>::infinity());
  18.  
  19.   	cout << "Lower bound:       " << f << "\nUpper bound:       " << d << "\nPrecision loss:    " << abs(d - f) << "\n\n";
  20.   } else {
  21.     const double f = nextafter(d, numeric_limits<double>::infinity());
  22.  
  23.   	cout << "Lower bound:       " << d << "\nUpper bound:       " << f << "\nPrecision loss:    " << abs(d - f) << "\n\n";
  24.  
  25.   }
  26. }
  27.  
  28. int main() {
  29.   f(numeric_limits<uint64_t>::max());         // Rounds up
  30.   f(numeric_limits<uint64_t>::max() - 2046);  // Rounds down
  31. }
Success #stdin #stdout 0s 4424KB
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stdin
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Standard input is empty
stdout
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Original:          18446744073709551615
Lower bound:       18446744073709549568
Upper bound:       18446744073709551616
Precision loss:    2048

Original:          18446744073709549569
Lower bound:       18446744073709549568
Upper bound:       18446744073709551616
Precision loss:    2048
https://ideone.com/DaRTzf
language:
C++ (gcc 8.3)
created:
6 years ago
visibility:
public

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