Merge pull request #904 from kvedala/fix/double_factorial

bug fix: fix self-tests and unsigned comparision to zero

math/double_factorial.cpp

@@ -1,8 +1,9 @@
 /**
  * @file
- * @brief Compute double factorial: \f$n!!\f$
+ * @brief Compute [double
+ * factorial](https://en.wikipedia.org/wiki/Double_factorial): \f$n!!\f$
  *
- * Double factorial of a non-negative integer n, is defined as the product of
+ * 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
  * \f$n!!\f$
@@ -32,10 +33,38 @@ uint64_t double_factorial_recursive(uint64_t n) {
     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);
+/** Wrapper to run tests using both recursive and iterative implementations.
+ * The checks are only valid in debug builds due to the use of `assert()`
+ * statements.
+ * \param [in] n number to check double factorial for
+ * \param [in] expected expected result
+ */
+void test(uint64_t n, uint64_t expected) {
+    assert(double_factorial_iterative(n) == expected);
+    assert(double_factorial_recursive(n) == expected);
+}
+
+/**
+ * Test implementations
+ */
+void tests() {
+    std::cout << "Test 1:\t n=5\t...";
+    test(5, 15);
+    std::cout << "passed\n";
+
+    std::cout << "Test 2:\t n=15\t...";
+    test(15, 2027025);
+    std::cout << "passed\n";
+
+    std::cout << "Test 3:\t n=0\t...";
+    test(0, 1);
+    std::cout << "passed\n";
+}
+
+/**
+ * Main function
+ */
+int main() {
+    tests();
+    return 0;
 }