documentation for double_factorial

math/double_factorial.cpp

@@ -1,28 +1,33 @@
-#include <iostream>
+/**
+ * @file
+ * Double factorial of a non-negative integer n, is defined as the product of
+ * all the integers from 1 to n that have the same parity (odd or even) as n.
+ * <br/>It is also called as semifactorial of a number and is denoted by `!!`
+ */
+
 #include <cassert>
+#include <iostream>
 
-/* Double factorial of a non-negative integer n, is defined as the product of 
-all the integers from 1 to n that have the same parity (odd or even) as n.
-It is also called as semifactorial of a number and is denoted by !! */
-
+/// Compute double factorial using iterative method
 uint64_t double_factorial_iterative(uint64_t n) {
-  uint64_t res = 1;
-  for ( uint64_t i = n; i >= 0; i -= 2 ) {
-    if (i == 0 || i == 1) return res;
-    res *= i;
-  }
+    uint64_t res = 1;
+    for (uint64_t i = n; i >= 0; i -= 2) {
+        if (i == 0 || i == 1) return res;
+        res *= i;
+    }
 }
 
-/* Recursion can be costly for large numbers */
-
+/// Compute double factorial using resursive method.
+//  <br/>Recursion can be costly for large numbers.
 uint64_t double_factorial_recursive(uint64_t n) {
-  if (n <= 1) return 1;
-  return n * double_factorial_recursive(n - 2);
+    if (n <= 1) return 1;
+    return n * double_factorial_recursive(n - 2);
 }
 
+/// main function
 int main() {
-  uint64_t n{};
-  std::cin >> n;
-  assert(n >= 0);
-  std::cout << double_factorial_iterative(n);
+    uint64_t n{};
+    std::cin >> n;
+    assert(n >= 0);
+    std::cout << double_factorial_iterative(n);
 }