Salieri: shader cache (#1701)

Here come Salieri, my implementation of a disk shader cache!

"I'm sure you know why I named it that."
"It doesn't really mean anything."

This implementation collects shaders at runtime and cache them to be later compiled when starting a game.

Ryujinx.Graphics.Gpu/Shader/Cache/Definition/CacheManifestHeader.cs

@@ -0,0 +1,97 @@
+using System;
+using System.Runtime.InteropServices;
+
+namespace Ryujinx.Graphics.Gpu.Shader.Cache.Definition
+{
+    /// <summary>
+    /// Header of the shader cache manifest.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1, Size = 0x10)]
+    struct CacheManifestHeader
+    {
+        /// <summary>
+        /// The version of the cache.
+        /// </summary>
+        public ulong Version;
+
+        /// <summary>
+        /// The graphics api used for this cache.
+        /// </summary>
+        public CacheGraphicsApi GraphicsApi;
+
+        /// <summary>
+        /// The hash type used for this cache.
+        /// </summary>
+        public CacheHashType HashType;
+
+        /// <summary>
+        /// CRC-16 checksum over the data in the file.
+        /// </summary>
+        public ushort TableChecksum;
+
+        /// <summary>
+        /// Construct a new cache manifest header.
+        /// </summary>
+        /// <param name="version">The version of the cache</param>
+        /// <param name="graphicsApi">The graphics api used for this cache</param>
+        /// <param name="hashType">The hash type used for this cache</param>
+        public CacheManifestHeader(ulong version, CacheGraphicsApi graphicsApi, CacheHashType hashType)
+        {
+            Version = version;
+            GraphicsApi = graphicsApi;
+            HashType = hashType;
+            TableChecksum = 0;
+        }
+
+        /// <summary>
+        /// Update the checksum in the header.
+        /// </summary>
+        /// <param name="data">The data to perform the checksum on</param>
+        public void UpdateChecksum(ReadOnlySpan<byte> data)
+        {
+            TableChecksum = CalculateCrc16(data);
+        }
+
+        /// <summary>
+        /// Calculate a CRC-16 over data.
+        /// </summary>
+        /// <param name="data">The data to perform the CRC-16 on</param>
+        /// <returns>A CRC-16 over data</returns>
+        private static ushort CalculateCrc16(ReadOnlySpan<byte> data)
+        {
+            int crc = 0;
+
+            const ushort poly = 0x1021;
+
+            for (int i = 0; i < data.Length; i++)
+            {
+                crc ^= data[i] << 8;
+
+                for (int j = 0; j < 8; j++)
+                {
+                    crc <<= 1;
+
+                    if ((crc & 0x10000) != 0)
+                    {
+                        crc = (crc ^ poly) & 0xFFFF;
+                    }
+                }
+            }
+
+            return (ushort)crc;
+        }
+
+        /// <summary>
+        /// Check the validity of the header.
+        /// </summary>
+        /// <param name="version">The target version in use</param>
+        /// <param name="graphicsApi">The target graphics api in use</param>
+        /// <param name="hashType">The target hash type in use</param>
+        /// <param name="data">The data after this header</param>
+        /// <returns>True if the header is valid</returns>
+        public bool IsValid(ulong version, CacheGraphicsApi graphicsApi, CacheHashType hashType, ReadOnlySpan<byte> data)
+        {
+            return Version == version && GraphicsApi == graphicsApi && HashType == hashType && TableChecksum == CalculateCrc16(data);
+        }
+    }
+}