luna: Introduce safe arithmetic operations, which return an error if an operation would overflow

luna/include/luna/SafeArithmetic.h

@@ -0,0 +1,38 @@
+#pragma once
+#include <luna/Result.h>
+
+template <typename T> constexpr bool add_will_overflow(T a, T b)
+{
+    return __builtin_add_overflow_p(a, b, (T)0);
+}
+
+template <typename T> constexpr bool sub_will_overflow(T a, T b)
+{
+    return __builtin_sub_overflow_p(a, b, (T)0);
+}
+
+template <typename T> constexpr bool mul_will_overflow(T a, T b)
+{
+    return __builtin_mul_overflow_p(a, b, (T)0);
+}
+
+template <typename T> Result<T> safe_add(T a, T b)
+{
+    if (add_will_overflow(a, b)) return err(EOVERFLOW);
+
+    return a + b;
+}
+
+template <typename T> Result<T> safe_sub(T a, T b)
+{
+    if (sub_will_overflow(a, b)) return err(EOVERFLOW);
+
+    return a - b;
+}
+
+template <typename T> Result<T> safe_mul(T a, T b)
+{
+    if (mul_will_overflow(a, b)) return err(EOVERFLOW);
+
+    return a * b;
+}