feat: add timer calibration

kernel/include/util/optional.h

@@ -9,6 +9,9 @@
 // instead of <utility>. The CrackOS3 value_or_panic() helper is omitted because
 // there is no global panic() in this tree yet.
 
+struct nullopt_t {};
+inline constexpr nullopt_t nullopt{};
+
 template<typename T>
 struct optional {
 private:
@@ -26,6 +29,7 @@ public:
     using value_type = T;
 
     constexpr optional() : initialized(false) {}
+    constexpr optional(nullopt_t) : initialized(false) {}
     optional(const T& value) : initialized(true) {
         new (buffer) T(value);
     }
@@ -135,10 +139,45 @@ public:
         return !initialized;
     }
 
-    template<typename R, typename Func, typename... ArgT>
-    optional<R> map(Func func, ArgT... args) {
+    template<typename Func>
+    auto map(Func&& func) -> optional<decltype(func(value()))> {
         if (initialized) {
-            return func(value(), forward<ArgT>(args)...);
+            return func(value());
+        } else {
+            return {};
+        }
+    }
+
+    template<typename Func>
+    auto map(Func&& func) const -> optional<decltype(func(value()))> {
+        if (initialized) {
+            return func(value());
+        } else {
+            return {};
+        }
+    }
+
+    template<typename Func>
+    optional or_else(Func&& func) const {
+        if (initialized) {
+            return *this;
+        }
+        return func();
+    }
+
+    template<typename Func>
+    auto bind(Func&& func) -> decltype(func(value())) {
+        if (initialized) {
+            return func(value());
+        } else {
+            return {};
+        }
+    }
+
+    template<typename Func>
+    auto bind(Func&& func) const -> decltype(func(value())) {
+        if (initialized) {
+            return func(value());
         } else {
             return {};
         }