Move types

src/Ryujinx.Horizon/Sdk/Hid/SharedMemory/Common/ISampledDataStruct.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Buffers.Binary;
+using System.Runtime.InteropServices;
+
+namespace Ryujinx.Horizon.Sdk.Hid.SharedMemory.Common
+{
+    /// <summary>
+    /// This is a "marker interface" to add some compile-time safety to a convention-based optimization.
+    ///
+    /// Any struct implementing this interface should:
+    ///   - use <c>StructLayoutAttribute</c> (and related attributes) to explicity control how the struct is laid out in memory.
+    ///   - ensure that the method <c>ISampledDataStruct.GetSamplingNumberFieldOffset()</c> correctly returns the offset, in bytes,
+    ///     to the ulong "Sampling Number" field within the struct. Most types have it as the first field, so the default offset is 0.
+    ///
+    /// Example:
+    ///
+    /// <c>
+    ///         [StructLayout(LayoutKind.Sequential, Pack = 8)]
+    ///         struct DebugPadState : ISampledDataStruct
+    ///         {
+    ///             public ulong SamplingNumber;    // 1st field, so no need to add special handling to GetSamplingNumberFieldOffset()
+    ///             // other members...
+    ///         }
+    ///
+    ///         [StructLayout(LayoutKind.Sequential, Pack = 8)]
+    ///         struct SixAxisSensorState : ISampledDataStruct
+    ///         {
+    ///             public ulong DeltaTime;
+    ///             public ulong SamplingNumber;    // Not the first field - needs special handling in GetSamplingNumberFieldOffset()
+    ///             // other members...
+    ///         }
+    /// </c>
+    /// </summary>
+    internal interface ISampledDataStruct
+    {
+        // No Instance Members - marker interface only
+
+        public static ulong GetSamplingNumber<T>(ref T sampledDataStruct) where T : unmanaged, ISampledDataStruct
+        {
+            ReadOnlySpan<T> structSpan = MemoryMarshal.CreateReadOnlySpan(ref sampledDataStruct, 1);
+
+            ReadOnlySpan<byte> byteSpan = MemoryMarshal.Cast<T, byte>(structSpan);
+
+            int fieldOffset = GetSamplingNumberFieldOffset(ref sampledDataStruct);
+
+            if (fieldOffset > 0)
+            {
+                byteSpan = byteSpan[fieldOffset..];
+            }
+
+            ulong value = BinaryPrimitives.ReadUInt64LittleEndian(byteSpan);
+
+            return value;
+        }
+
+        private static int GetSamplingNumberFieldOffset<T>(ref T sampledDataStruct) where T : unmanaged, ISampledDataStruct
+        {
+            return sampledDataStruct switch
+            {
+                Npad.SixAxisSensorState _ => sizeof(ulong),
+                _ => 0,
+            };
+        }
+    }
+}