merge doublemelon (#2067)

non-exhaustive (but exhausting) list of changes:

* base laid for multiple window support, but will likely require more work to work correctly
* encapsulation of frontend state for proper multi-instance support
* (JIT still needs a fix for the NDS::Current workaround but we can get there later)
* new, more flexible configuration system

src/FIFO.h

@@ -24,6 +24,7 @@
 
 namespace melonDS
 {
+
 template<typename T, u32 NumEntries>
 class FIFO
 {
@@ -191,5 +192,121 @@ private:
     u32 ReadPos, WritePos;
 };
 
+template<u32 Size>
+class RingBuffer
+{
+public:
+    void Clear()
+    {
+        NumOccupied = 0;
+        ReadPos = 0;
+        WritePos = 0;
+        memset(Buffer, 0, Size);
+    }
+
+
+    void DoSavestate(Savestate* file)
+    {
+        file->Var32(&NumOccupied);
+        file->Var32(&ReadPos);
+        file->Var32(&WritePos);
+
+        file->VarArray(Buffer, Size);
+    }
+
+
+    bool Write(const void* data, u32 len)
+    {
+        if (!CanFit(len)) return false;
+
+        if ((WritePos + len) >= Size)
+        {
+            u32 part1 = Size - WritePos;
+            memcpy(&Buffer[WritePos], data, part1);
+            if (len > part1)
+                memcpy(Buffer, &((u8*)data)[part1], len - part1);
+            WritePos = len - part1;
+        }
+        else
+        {
+            memcpy(&Buffer[WritePos], data, len);
+            WritePos += len;
+        }
+
+        NumOccupied += len;
+
+        return true;
+    }
+
+    bool Read(void* data, u32 len)
+    {
+        if (NumOccupied < len) return false;
+
+        u32 readpos = ReadPos;
+        if ((readpos + len) >= Size)
+        {
+            u32 part1 = Size - readpos;
+            memcpy(data, &Buffer[readpos], part1);
+            if (len > part1)
+                memcpy(&((u8*)data)[part1], Buffer, len - part1);
+            ReadPos = len - part1;
+        }
+        else
+        {
+            memcpy(data, &Buffer[readpos], len);
+            ReadPos += len;
+        }
+
+        NumOccupied -= len;
+        return true;
+    }
+
+    bool Peek(void* data, u32 offset, u32 len)
+    {
+        if (NumOccupied < len) return false;
+
+        u32 readpos = ReadPos + offset;
+        if (readpos >= Size) readpos -= Size;
+
+        if ((readpos + len) >= Size)
+        {
+            u32 part1 = Size - readpos;
+            memcpy(data, &Buffer[readpos], part1);
+            if (len > part1)
+                memcpy(&((u8*)data)[part1], Buffer, len - part1);
+        }
+        else
+        {
+            memcpy(data, &Buffer[readpos], len);
+        }
+
+        return true;
+    }
+
+    bool Skip(u32 len)
+    {
+        if (NumOccupied < len) return false;
+
+        ReadPos += len;
+        if (ReadPos >= Size)
+            ReadPos -= Size;
+
+        NumOccupied -= len;
+        return true;
+    }
+
+    u32 Level() const { return NumOccupied; }
+    bool IsEmpty() const { return NumOccupied == 0; }
+    bool IsFull() const { return NumOccupied >= Size; }
+
+    bool CanFit(u32 num) const { return ((NumOccupied + num) <= Size); }
+
+private:
+    u8 Buffer[Size] = {0};
+    u32 NumOccupied = 0;
+    u32 ReadPos = 0, WritePos = 0;
+};
+
 }
+
 #endif