To create a random number engine that generates prime number on the go!
primeDB
fileC++
already have random engines, Let us create a wrapper around that using templates()
-> returns random prime numbermin()
-> returns min prime numbermax()
-> returns max prime number<<
-> save the state to std::stringstream
>>
-> restores the state from std::stringstream
template <typename Engine> Engine eng;
int min_prime;
int max_prime;
char const *db_filepath;
Constructor
int operator()();
friend stringstream &operator<<
friend stringstream &operator>>
seed
and filepath
#define DB_FILEPATH "primeDB"
template <typename Engine>
random_prime_engine<Engine>::random_prime_engine(unsigned long rand_seed, char const *db_filepath=DB_FILEPATH)
{
// Get DB path
this->db_filepath = db_filepath;
eng.seed(rand_seed);
}
// Usage
ra::random_prime_engine<std::default_random_engine> rpe_2(rand_seed);
()
operator,#define DB_SIZE 10000
template <typename Engine>
int random_prime_engine<Engine>::operator()()
{
int idx = eng() % DB_SIZE; // to get a index within file
int rand_prime;
// Open the file
std::ifstream file;
file.open(db_filepath);
// update rand_prime till it gets the value at index
for (int i = 0; i <= idx; i++)
file >> rand_prime;
file.close();
return (rand_prime);
}
// Usage
std::cout << rpe()
# pseudo code
# initialize min/max with 0, for lazy initialization
{
# return min or max if once found
if bool(min/max):
return min/max
min = file.first_line
max = file.last_line
return min/max
}
>>
and <<
// Friend Functions
#define stringstream SS
function SS &operator<>(SS&in/out, rpe){
in/out >> rpe.eng;
return in/out
}
// Usage
std::stringstream state;
state << rpe; //save current state
state >> rpe; //restore old state