Actually add offset_ptr.h to the repo

include/dusk/offset_ptr.h

@@ -0,0 +1,67 @@
+#ifndef DUSK_OFFSET_PTR_H
+#define DUSK_OFFSET_PTR_H
+
+#if TARGET_PC
+
+#include "global.h"
+#include "endian.h"
+
+struct OffsetPtr {
+    // Top bit is used to store "already relocated" flag as a guard thing.
+    BE<s32> value;
+
+    bool setBase(void* base);
+    bool isRelocated();
+
+    template<typename T>
+    explicit operator T*() const {
+        s32 swapped = value;
+        if (swapped == 0) {
+            // This shouldn't be able to happen but the original offsetting code has the safeguard.
+            return nullptr;
+        }
+
+        // Because we use the top (31st) bit as an "already relocated" flag,
+        // we need to make sure to check the 30th bit to see if we're actually negative.
+        // And cut off the 31st bit if we're supposed to be positive.
+        // Effective range this gives us is still like a gigabyte in both directions,
+        // so we'll be fine on that front.
+        s32 realOffset = (swapped & 0x4000'0000) ? swapped : (swapped & 0x7FFF'FFFF);
+        return (T*)POINTER_ADD(this, realOffset);
+    }
+};
+
+template<typename T>
+struct OffsetPtrT {
+    OffsetPtr value;
+
+    bool setBase(void* base) {
+        return value.setBase(base);
+    }
+    bool isRelocated() {
+        return value.isRelocated();
+    }
+
+    T* operator->() {
+        return (T*) value;
+    }
+
+    operator T*() const {
+        return (T*) value;
+    }
+
+    template<typename TOther>
+    explicit operator TOther*() const {
+        return (TOther*) value;
+    }
+};
+
+
+#define OFFSET_PTR(T) OffsetPtrT<T>
+#define OFFSET_PTR_RAW OffsetPtr
+#else
+#define OFFSET_PTR(T) T*
+#define OFFSET_PTR_RAW u32
+#endif
+
+#endif  // DUSK_OFFSET_PTR_H