fork download
copy 
  1. #include <iostream>
  2. #include <stdexcept>
  3. #include <limits>
  4.  
  5. // tons of ways to make this faster on the bithacks page
  6. int maxbitpos(int n) // assume positive
  7. {
  8.     int p = 0;
  9.     while(n >>= 1) ++p;
  10.     return p;
  11. }
  12.  
  13. // doing power as n*n*n*n*n*... is as pointless as bubble sort
  14. int mypow(int n, int p)
  15. {
  16.     if(p<0) 
  17.         throw std::runtime_error("negative power not supported");
  18.     if(p==0) return 1; // not hanlding negative powers for this
  19.     if(p==1) return n; // avoid overflow in squaring
  20.  
  21.     if(2*maxbitpos(n) >= std::numeric_limits<int>::digits)
  22.         throw std::overflow_error("integer overflow in pow()");
  23.  
  24.     int r = mypow(n*n, p/2);
  25.  
  26.     if(p&1) {
  27.         if(maxbitpos(n) + maxbitpos(r) >= std::numeric_limits<int>::digits)
  28.             throw std::overflow_error("integer overflow in pow()");
  29.         return n*r;
  30.     } else {
  31.         return r;
  32.     }
  33. }
  34.  
  35. int main()
  36. {
  37.     for(;;) {
  38.         std::cout << "integer: ";
  39.         int n;
  40.         std::cin >> n;
  41.  
  42.         std::cout << "power: ";
  43.         int p;
  44.         std::cin >> p;
  45.  
  46.         if(!std::cin) break; // quit on EOF
  47.  
  48.         try {
  49.             std::cout << "result = " << mypow(n, p) << '\n';
  50.         } catch(const std::exception& e) {
  51.             std::cout << "could not pow(): " << e.what() << '\n';
  52.         }
  53.     }
  54. }
  55.  
Success #stdin #stdout 0.02s 2864KB
comments (?)
stdin
copy 
2
10
10
10
2
30
2
31
stdout
copy 
integer: power: result = 1024
integer: power: could not pow(): integer overflow in pow()
integer: power: result = 1073741824
integer: power: could not pow(): integer overflow in pow()
integer: power:
https://ideone.com/x94na
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!