Aim:
To create a random number engine that generates prime number on the go! Here the link GitHub repo
Plan of Attack:
- Since finding prime number in constant time is impossible by the math at the moment, So We are going to use a database-based approach. Lets store all the prime number in
primeDBfile - Since
C++already have random engines, Let us create a wrapper around that using templates
Objective:
- Container that takes in engine class and override all the engine functions, also takes in filepath for database
- Functions to override
-
()-> returns random prime number -
min()-> returns min prime number -
max()-> returns max prime number -
<<-> save the state tostd::stringstream -
>>-> restores the state fromstd::stringstream
-
Code:
-
Private Members:
template <typename Engine> Engine eng;int min_prime;int max_prime;char const *db_filepath;
-
Public Members:
Constructorint operator()();friend stringstream &operator<<friend stringstream &operator>>
Constructor: takes in 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()
min and max
# 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
All the code can be found at the below link:
https://github.com/ra101/Random-Prime-Number-Generator-Engine-cpp
Top comments (0)