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  1. #include <iostream>
  2.  
  3. typedef unsigned long long BIG;
  4. BIG mod_multiply( BIG A, BIG B, BIG C )
  5. {
  6.     BIG mod_product = 0;
  7.     // A %= C; may or may not help performance
  8.     B %= C;
  9.  
  10.     while (A) {
  11.         if (A & 1) {
  12.             mod_product += B;
  13.             if (mod_product > C) mod_product -= C;
  14.         }
  15.         A >>= 1;
  16.         B <<= 1;
  17.         if (B > C) B -= C;
  18.     }
  19.  
  20.     return mod_product;
  21. }
  22.  
  23. int main()
  24. {
  25.     uint64_t retval = mod_multiply( 19010000000000000000, 1011000000000000, 1231231231231211 );
  26.     std::cout << retval << "\n";
  27. }
Success #stdin #stdout 0s 2852KB
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946004848926081
https://ideone.com/1pTldb
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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