Add helper function for unsigned saturating add

src/core/math_func.hpp

@@ -414,6 +414,26 @@ constexpr uint64_t PowerOfTen(int power)
 	return result;
 }
 
+/**
+ * Unsigned saturating add.
+ */
+template<typename T, std::enable_if_t<std::is_unsigned_v<T>, int> = 0>
+constexpr inline T SaturatingAdd(T a, T b)
+{
+#ifdef WITH_OVERFLOW_BUILTINS
+	T c;
+	if (unlikely(__builtin_add_overflow(a, b, &c))) {
+		return std::numeric_limits<T>::max();
+	}
+	return c;
+#else
+	T c = a + b;
+	if (c < a) return std::numeric_limits<T>::max();
+	return c;
+#endif
+}
+
+
 uint32_t IntSqrt(uint32_t num);
 uint32_t IntSqrt64(uint64_t num);
 uint32_t IntCbrt(uint64_t num);

src/tests/math_func.cpp

@@ -95,3 +95,13 @@ TEST_CASE("SoftClamp")
 	CHECK(1250 * million == SoftClamp(0, 1500 * million, 1000 * million));
 	CHECK(0 == SoftClamp(0, 1500 * million, -1500 * million));
 }
+
+TEST_CASE("SaturatingAdd")
+{
+	CHECK(SaturatingAdd<uint8_t>(2, 3) == 5);
+	CHECK(SaturatingAdd<uint8_t>(200, 200) == 255);
+	CHECK(SaturatingAdd<uint8_t>(255, 255) == 255);
+	CHECK(SaturatingAdd<uint8_t>(1, 255) == 255);
+	CHECK(SaturatingAdd<uint8_t>(255, 1) == 255);
+	CHECK(SaturatingAdd<uint8_t>(0, 254) == 254);
+}