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  1. /*
  2. Function to get the maximum possible number of places a numeric type could hypothetically represent under ideal circumstances.
  3. Copyright (C) 2015 Peter R. Bloomfield
  4. Web: avidinsight.uk
  5.  
  6. This code is made freely available under the terms of the MIT open source license.
  7. */
  8.  
  9. #include <iostream>
  10. #include <cmath>
  11. #include <limits>
  12.  
  13. using namespace std;
  14.  
  15. // Get the maximum number of radix 
  16. template <typename T_type, int T_radix>
  17. int getMaxPlaces()
  18. {
  19.     static_assert(
  20.         T_radix > 1,
  21.         "Radix must be at least 2."
  22.     );
  23.     static_assert(
  24.         std::numeric_limits<T_type>::is_specialized,
  25.         "Numeric limits traits info not found."
  26.     );
  27.  
  28.     // Integers contain no point.
  29.     if (std::numeric_limits<T_type>::is_integer)
  30.         return 0;
  31.  
  32.     // Maximum number of places in the native radix.
  33.     const int places =
  34.         std::abs(std::numeric_limits<T_type>::min_exponent) +
  35.         std::numeric_limits<T_type>::digits;
  36.  
  37.     // Special case: If the requested radix matches the underlying radix
  38.     //  specified in traits then no base conversion is necessary.
  39.     if (T_radix == std::numeric_limits<T_type>::radix)
  40.         return places;
  41.  
  42.     // Convert the number of places to the requested radix.
  43.     return static_cast<int>( std::ceil(
  44.         places *
  45.         std::log(std::numeric_limits<T_type>::radix) /
  46.         std::log(T_radix)
  47.     ));
  48. }
  49.  
  50. int main() {
  51. 	cout << "int:         " << getMaxPlaces<int, 10>() << endl;
  52. 	cout << "float:       " << getMaxPlaces<float, 10>() << endl;
  53. 	cout << "double:      " << getMaxPlaces<double, 10>() << endl;
  54. 	cout << "long double: " << getMaxPlaces<long double, 10>() << endl;
  55. 	return 0;
  56. }
Success #stdin #stdout 0s 3456KB
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stdin
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Standard input is empty
stdout
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int:         0
float:       45
double:      324
long double: 4951
https://ideone.com/NNsHwn
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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