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  1. #include <iostream>
  2. #include <limits>
  3. #include <cmath>
  4. using namespace std;
  5.  
  6.  
  7. double large_exp_quot2(
  8. 	double const eNum,
  9. 	double const eDenom,
  10. 	int & scale) {
  11.   double const eExponent = eNum - eDenom;
  12.   double tExponent = eExponent * log10(exp(1));
  13.   scale = 0;
  14.   if (tExponent >= numeric_limits<double>::max_exponent10) {
  15.   	do {
  16.   	  tExponent -= numeric_limits<double>::max_exponent10;
  17.   	  scale += numeric_limits<double>::max_exponent10;
  18.   	} while(tExponent >= numeric_limits<double>::max_exponent10);
  19.   	return pow(10, tExponent);
  20.   }
  21.   else if (tExponent <= numeric_limits<double>::min_exponent10) {
  22.   	do {
  23.       tExponent -= numeric_limits<double>::min_exponent10;
  24.       scale += numeric_limits<double>::min_exponent10;
  25.   	} while (tExponent <= numeric_limits<double>::min_exponent10);
  26.     return pow(10, tExponent);
  27.   }
  28.   return exp(eExponent);
  29. }
  30.  
  31. double large_exp_quot(
  32.     double eNum,
  33.     double eDenom,
  34.     unsigned int const critical = 200) {
  35.   if (abs(eNum - eDenom) > critical) {
  36.   	throw out_of_range{"That won't work, resulting exponent is too large"};
  37.   }
  38.   unsigned int eDivisor = 1;
  39.   while (abs(eNum) > critical or abs(eDenom) > critical) {
  40.     eNum /= 2;
  41.     eDenom /= 2;
  42.     eDivisor *= 2;
  43.   }
  44.   return pow(exp(eNum) / exp(eDenom), eDivisor);
  45. }
  46.  
  47. int main() {
  48. 	int scale;
  49. 	double const result = large_exp_quot2(90000, 100, scale);
  50. 	double const exponent = round(log10(result));
  51. 	scale += exponent;
  52. 	cout
  53. 	  << "exp(90000) / exp(100)  =  "
  54. 	  << (result / pow(10, exponent)) << " scaled by 10^" << scale << endl;
  55. 	return 0;
  56. }
Success #stdin #stdout 0s 3460KB
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exp(90000) / exp(100)  =  1.18556 scaled by 10^39043
https://ideone.com/WvKLJG
quotient of large exponentials
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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