From af5156f6ef1b8b87593b5acd005b13a07baabf36 Mon Sep 17 00:00:00 2001
From: Blue <bluestorm.android@gmail.com>
Date: Sat, 29 May 2021 17:44:36 +0200
Subject: [PATCH] Add: Sector, an spanized buffer/queue. The CDROM doesn't need
 a real tail/head queue/enqueue function, as it only needs to one shot the
 fill of the sector and then dequeue. Also Queue<T> doesn't have a Span<T>
 constructor and can't clean and "addAll" without allocating a new internal
 buffer array. This little util class aims to try to avoid allocations as well
 as simplify the DMAs out.

---
 ProjectPSX/Devices/CDROM/Sector.cs | 42 ++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 ProjectPSX/Devices/CDROM/Sector.cs

diff --git a/ProjectPSX/Devices/CDROM/Sector.cs b/ProjectPSX/Devices/CDROM/Sector.cs
new file mode 100644
index 0000000..b9b196d
--- /dev/null
+++ b/ProjectPSX/Devices/CDROM/Sector.cs
@@ -0,0 +1,42 @@
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace ProjectPSX.Devices.CdRom {
+    class Sector {
+
+        private const int BYTES_PER_SECTOR_RAW = 2352;
+        private byte[] sectorBuffer = new byte[BYTES_PER_SECTOR_RAW];
+
+        private int pointer;
+        private int size;
+
+        public void fillWith(Span<byte> data) {
+            pointer = 0;
+            size = data.Length;
+            var dest = sectorBuffer.AsSpan();
+            data.CopyTo(dest);
+        }
+
+        public ref byte readByte() {
+            ref var data = ref MemoryMarshal.GetArrayDataReference(sectorBuffer);
+            return ref Unsafe.Add(ref data, pointer++);
+        }
+
+        public Span<uint> read(int size) { //size from dma comes as u32
+            var dma = sectorBuffer.AsSpan().Slice(pointer, size * 4);
+            pointer += size * 4;
+            return MemoryMarshal.Cast<byte, uint>(dma);
+        }
+
+        public Span<byte> read() => sectorBuffer.AsSpan().Slice(0, size);
+
+        public bool hasData() => pointer < size;
+
+        public void clear() {
+            pointer = 0;
+            size = 0;
+        }
+
+    }
+}