compute arbitrarily large fibonacci number

others/fibonacci_large.cpp

@@ -0,0 +1,51 @@
+/**
+ * Computes N^th Fibonacci number given as
+ * input argument. Uses custom build arbitrary integers library
+ * to perform additions and other operations.
+ *
+ * Took 0.608246 seconds to compute 50,000^th Fibonacci
+ * number that contains 10450 digits!
+ **/
+
+#include "large_number.h"
+#include <iostream>
+#include <chrono>
+
+large_number fib(unsigned long long n)
+{
+    large_number f0(1);
+    large_number f1(1);
+
+    do
+    {
+        large_number f2 = f0 + f1;
+        f0 = f1;
+        f1 = f2;
+        n--;
+    } while (n > 2); // since we start from 2
+    return f1;
+}
+
+int main(int argc, char *argv[])
+{
+    unsigned long long N;
+    if (argc == 2)
+        N = strtoull(argv[1], NULL, 10);
+    else
+    {
+        std::cout << "Enter N: ";
+        std::cin >> N;
+    }
+
+    auto start_time = std::chrono::high_resolution_clock::now();
+    large_number result = fib(N);
+    auto end_time = std::chrono::high_resolution_clock::now();
+    std::chrono::duration<double> time_taken = end_time - start_time;
+
+    std::cout
+        << std::endl
+        << N << "^th Fibonacci number: " << result << std::endl
+        << "Number of digits: " << result.num_digits() << std::endl
+        << "Time taken: " << time_taken.count() << " s" << std::endl;
+    return 0;
+}