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  1. #include <iostream>
  2. #include <cassert>
  3. #include <chrono>
  4. #include <random>
  5.  
  6. typedef long long ll;
  7.  
  8. const int mod = 2147483647;
  9.  
  10. // Calculate x % (2^31-1) fast
  11. // 0 <= x <= (2^31-2)^2
  12. inline int fast_mod(ll value) {
  13.     value = (value >> 31) + (value & mod);
  14.     value = (value >> 31) + (value & mod);
  15.     return value == mod ? 0 : value;
  16. }
  17.  
  18. int main() {
  19.     auto seed = std::chrono::high_resolution_clock::now().time_since_epoch().count();
  20.     std::mt19937 mt_rand(seed);
  21.     std::uniform_int_distribution<ll> dis(ll(1e9), ll(1e18));
  22.  
  23.     for (int n = 0; n < 100000000; ++n) {
  24.         ll value = dis(mt_rand);
  25.         assert(value % mod == fast_mod(value));
  26.     }
  27.     std::cout << "ok!";
  28.     return 0;
  29. }
Success #stdin #stdout 3.12s 4496KB
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ok!
https://ideone.com/FWZItw
language:
C++14 (gcc 8.3)
created:
5 years ago
visibility:
public

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