update the checked_multiply template to deal with mismatched sign in …

…signed numbers and min val correctly. This involved adding to templates to clear up warnings

include/CLI/Validators.hpp

@@ -509,12 +509,24 @@ auto search(const T &set, const V &val, const std::function<V(V)> &filter_functi
     });
     return {(it != std::end(setref)), it};
 }
-/// Generate the absolute value of a number
-template <typename T> inline typename std::enable_if<std::is_signed<T>::value, T>::type absval(T a) {
-    return static_cast<T>((std::abs)(a));
+
+// the following suggestion was made by Nikita Ofitserov(@himikof)
+// done in templates to prevent compiler warnings on negation of unsigned numbers
+
+/// Do a check for overflow on signed numbers
+template <typename T>
+inline typename std::enable_if<std::is_signed<T>::value, T>::type overflowCheck(const T &a, const T &b) {
+    if((a > 0) == (b > 0)) {
+        return ((std::numeric_limits<T>::max)() / (std::abs)(a) < (std::abs)(b));
+    } else {
+        return ((std::numeric_limits<T>::min)() / (std::abs)(a) > -(std::abs)(b));
+    }
+}
+/// Do a check for overflow on unsigned numbers
+template <typename T>
+inline typename std::enable_if<!std::is_signed<T>::value, T>::type overflowCheck(const T &a, const T &b) {
+    return ((std::numeric_limits<T>::max)() / a < b);
 }
-/// unsigned values just return the value
-template <typename T> inline typename std::enable_if<!std::is_signed<T>::value, T>::type absval(T a) { return a; }
 
 /// Performs a *= b; if it doesn't cause integer overflow. Returns false otherwise.
 template <typename T> typename std::enable_if<std::is_integral<T>::value, bool>::type checked_multiply(T &a, T b) {
@@ -525,7 +537,7 @@ template <typename T> typename std::enable_if<std::is_integral<T>::value, bool>:
     if(a == (std::numeric_limits<T>::min)() || b == (std::numeric_limits<T>::min)()) {
         return false;
     }
-    if((std::numeric_limits<T>::max)() / absval(a) < absval(b)) {
+    if(overflowCheck(a, b)) {
         return false;
     }
     a *= b;

tests/HelpersTest.cpp

@@ -437,6 +437,20 @@ TEST(CheckedMultiply, Int) {
     b = -101;
     ASSERT_FALSE(CLI::detail::checked_multiply(a, b));
     ASSERT_EQ(a, std::numeric_limits<int>::min() / 100);
+    a = 2;
+    b = std::numeric_limits<int>::min() / 2;
+    ASSERT_TRUE(CLI::detail::checked_multiply(a, b));
+    a = std::numeric_limits<int>::min() / 2;
+    b = 2;
+    ASSERT_TRUE(CLI::detail::checked_multiply(a, b));
+
+    a = 4;
+    b = std::numeric_limits<int>::min() / 4;
+    ASSERT_TRUE(CLI::detail::checked_multiply(a, b));
+
+    a = 48;
+    b = std::numeric_limits<int>::min() / 48;
+    ASSERT_TRUE(CLI::detail::checked_multiply(a, b));
 }
 
 TEST(CheckedMultiply, SizeT) {