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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. long long mul(long long a, long long b, long long p) {
  5. 	long long k = (long long)((long double)a * b / p + 0.5);
  6. 	return a * b - k * p;
  7. }
  8.  
  9.  
  10. int main() {
  11. 	long long m = 1e11 + 7;
  12.  
  13. 	long long a = 1e11 - 1;
  14. 	long long b = mul(a, a, m);
  15. 	cout << b << endl;	//correct
  16.  
  17. 	long double c = a;
  18. 	long double d = fmod(c * c, m);
  19. 	cout << d << endl;	//wrong
  20.  
  21. 	return 0;
  22. }
Success #stdin #stdout 0s 15240KB
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stdin 
Standard input is empty
stdout 
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https://ideone.com/GiVgj3
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
secret

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