+/*
+ * Complementary type traits for integral comparisons.
+ *
+ * For instance, `if(x < 0)` yields an error in clang for unsigned types
+ * when -Werror is used due to -Wtautological-compare
+ *
+ *
+ * @author: Marcelo Juchem <marcelo@fb.com>
+ */
+
+namespace detail {
+
+template <typename T, bool>
+struct is_negative_impl {
+ constexpr static bool check(T x) { return x < 0; }
+};
+
+template <typename T>
+struct is_negative_impl<T, false> {
+ constexpr static bool check(T) { return false; }
+};
+
+// folly::to integral specializations can end up generating code
+// inside what are really static ifs (not executed because of the templated
+// types) that violate -Wsign-compare so suppress them in order to not prevent
+// all calling code from using it.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wsign-compare"
+
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than_impl(LHS const lhs) {
+ return
+ rhs > std::numeric_limits<LHS>::max() ? true :
+ rhs <= std::numeric_limits<LHS>::min() ? false :
+ lhs < rhs;
+}
+
+#pragma GCC diagnostic pop
+
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than_impl(LHS const lhs) {
+ return
+ rhs > std::numeric_limits<LHS>::max() ? false :
+ rhs < std::numeric_limits<LHS>::min() ? true :
+ lhs > rhs;
+}
+
+} // namespace detail {
+
+// same as `x < 0`
+template <typename T>
+constexpr bool is_negative(T x) {
+ return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
+}
+
+// same as `x <= 0`
+template <typename T>
+constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
+
+// same as `x > 0`
+template <typename T>
+constexpr bool is_positive(T x) { return !is_non_positive(x); }
+
+// same as `x >= 0`
+template <typename T>
+constexpr bool is_non_negative(T x) {
+ return !x || is_positive(x);
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than(LHS const lhs) {
+ return detail::less_than_impl<
+ RHS, rhs, typename std::remove_reference<LHS>::type
+ >(lhs);
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than(LHS const lhs) {
+ return detail::greater_than_impl<
+ RHS, rhs, typename std::remove_reference<LHS>::type
+ >(lhs);
+}
+