LibPDF: Extract reference bitpacking into dedicated class

Userland/Libraries/LibPDF/Reference.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2021, Matthew Olsson <mattco@serenityos.org>
+ * Copyright (c) 2021, Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace PDF {
+
+class Reference {
+    // We store refs as u32, with 18 bits for the index and 14 bits for the
+    // generation index. The generation index is stored in the higher bits.
+    // This may need to be rethought later, as the max generation index is
+    // 2^16 and the max for the object index is probably 2^32 (I don't know
+    // exactly)
+    static constexpr auto MAX_REF_INDEX = (1 << 19) - 1;            // 2 ^ 19 - 1
+    static constexpr auto MAX_REF_GENERATION_INDEX = (1 << 15) - 1; // 2 ^ 15 - 1
+
+public:
+    Reference(u32 index, u32 generation_index)
+    {
+        VERIFY(index < MAX_REF_INDEX);
+        VERIFY(generation_index < MAX_REF_GENERATION_INDEX);
+        m_combined = (generation_index << 14) | index;
+    }
+
+    [[nodiscard]] ALWAYS_INLINE u32 as_ref_index() const
+    {
+        return m_combined & 0x3ffff;
+    }
+
+    [[nodiscard]] ALWAYS_INLINE u32 as_ref_generation_index() const
+    {
+        return m_combined >> 18;
+    }
+
+private:
+    u32 m_combined;
+};
+
+}