chore: import upstream snapshot with attribution

math/fibonacci.cpp

@@ -0,0 +1,67 @@
+/**
+ * @file
+ * @brief n-th [Fibonacci
+ * number](https://en.wikipedia.org/wiki/Fibonacci_sequence).
+ *
+ * @details
+ * Naive recursive implementation to calculate the n-th Fibonacci number.
+ * \f[\text{fib}(n) = \text{fib}(n-1) + \text{fib}(n-2)\f]
+ *
+ * @see fibonacci_large.cpp, fibonacci_fast.cpp, string_fibonacci.cpp
+ */
+
+#include <cstdint>
+#include <cassert>   /// for assert
+#include <iostream>  /// for IO operations
+
+/**
+ * @namespace math
+ * @brief Math algorithms
+ */
+namespace math {
+/**
+ * @namespace fibonacci
+ * @brief Functions for Fibonacci sequence
+ */
+namespace fibonacci {
+/**
+ * @brief Function to compute the n-th Fibonacci number
+ * @param n the index of the Fibonacci number
+ * @returns n-th element of the Fibonacci's sequence
+ */
+uint64_t fibonacci(uint64_t n) {
+    // If the input is 0 or 1 just return the same (Base Case)
+    // This will set the first 2 values of the sequence
+    if (n <= 1) {
+        return n;
+    }
+
+    // Add the preceding 2 values of the sequence to get next
+    return fibonacci(n - 1) + fibonacci(n - 2);
+}
+}  // namespace fibonacci
+}  // namespace math
+
+/**
+ * @brief Self-test implementation
+ * @returns `void`
+ */
+static void test() {
+    assert(math::fibonacci::fibonacci(0) == 0);
+    assert(math::fibonacci::fibonacci(1) == 1);
+    assert(math::fibonacci::fibonacci(2) == 1);
+    assert(math::fibonacci::fibonacci(3) == 2);
+    assert(math::fibonacci::fibonacci(4) == 3);
+    assert(math::fibonacci::fibonacci(15) == 610);
+    assert(math::fibonacci::fibonacci(20) == 6765);
+    std::cout << "All tests have passed successfully!\n";
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    test();  // run self-test implementations
+    return 0;
+}