chore: import upstream snapshot with attribution

others/primality_test.cpp

@@ -0,0 +1,42 @@
+/**
+ * @file
+ * @brief [Primality test](https://en.wikipedia.org/wiki/Primality_test)
+ * implementation.
+ *
+ * A simple and efficient implementation of a function to test if a number is
+ * prime, based on the fact that
+ * > Every Prime number, except 2 and 3, are of the form \f$6k\pm1\f$ for
+ * > integer values of k.
+ * This gives a 3x speed improvement.
+ */
+#include <iostream>
+
+/** Check if a number is prime
+ * \param[in] number number to check
+ * \returns true if prime else false
+ */
+bool IsPrime(int number) {
+    if (((!(number & 1)) && number != 2) || (number < 2) ||
+        (number % 3 == 0 && number != 3))
+        return false;
+
+    for (int k = 1; 36 * k * k - 12 * k < number; ++k) {
+        if ((number % (6 * k + 1) == 0) || (number % (6 * k - 1) == 0))
+            return false;
+    }
+    return true;
+}
+
+/** main function */
+int main() {
+    // Main Function
+    std::cout << "Enter the value of n to check if Prime\n";
+    int n;
+    std::cin >> n;
+    if (IsPrime(n))
+        std::cout << n << " is Prime" << std::endl;
+    else
+        std::cout << n << " is not Prime" << std::endl;
+
+    return 0;
+}