Max speed (0.0ns) and safer ConstructRid

pkdawson · Sep 9, 2024 · 14e05b6 · 14e05b6
1 parent 14eb84c
commit 14e05b6
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Showing 2 changed files with 16 additions and 25 deletions.
diff --git a/addons/imgui-godot/ImGuiGodot/Internal/Util.cs b/addons/imgui-godot/ImGuiGodot/Internal/Util.cs
@@ -1,14 +1,15 @@
 using Godot;
 using System;
+using System.Runtime.InteropServices;
 
 namespace ImGuiGodot.Internal;
 
 internal static class Util
 {
-    public static unsafe Rid ConstructRid(ulong id)
+    public static Rid ConstructRid(ulong id)
     {
-        Rid rv;
-        Buffer.MemoryCopy(&id, &rv, sizeof(Rid), sizeof(ulong));
-        return rv;
+        ReadOnlySpan<ulong> uspan = new(in id);
+        ReadOnlySpan<byte> bytes = MemoryMarshal.Cast<ulong, byte>(uspan);
+        return MemoryMarshal.Read<Rid>(bytes);
     }
 }
diff --git a/doc/test/csbench/BenchRid.cs b/doc/test/csbench/BenchRid.cs
@@ -2,7 +2,6 @@
 using System.Reflection.Emit;
 using System.Reflection;
 using System.Runtime.InteropServices;
-using System.Runtime.CompilerServices;
 
 namespace csbench;
 
@@ -11,7 +10,6 @@ public class BenchRid
 {
     private readonly Func<ulong, Rid> _constructRid;
     private readonly ulong _id = 12345;
-    private readonly nint _buf;
 
     public BenchRid()
     {
@@ -25,11 +23,9 @@ public BenchRid()
         il.Emit(OpCodes.Newobj, cinfo);
         il.Emit(OpCodes.Ret);
         _constructRid = dm.CreateDelegate<Func<ulong, Rid>>();
-
-        _buf = Marshal.AllocHGlobal(Marshal.SizeOf<Rid>());
     }
 
-    [Benchmark(Baseline = true)]
+    [Benchmark]
     public Rid ConstructRid_Emitted()
     {
         return _constructRid(_id);
@@ -47,29 +43,23 @@ public Rid ConstructRid_Marshal()
     }
 
     [Benchmark]
-    public Rid ConstructRid_Marshal_PreAlloc()
+    public Rid ConstructRid_MemoryMarshal_WriteRead()
     {
-        // not thread-safe
-        byte[] bytes = BitConverter.GetBytes(_id);
-        Marshal.Copy(bytes, 0, _buf, bytes.Length);
-        Rid rv = Marshal.PtrToStructure<Rid>(_buf);
-        return rv;
+        Span<byte> bytes = stackalloc byte[sizeof(ulong)];
+        MemoryMarshal.TryWrite(bytes, in _id);
+        return MemoryMarshal.Read<Rid>(bytes);
     }
 
     [Benchmark]
-    public unsafe Rid ConstructRid_Unsafe()
+    public Rid ConstructRid_MemoryMarshal_SpanCast()
     {
-        Rid rv;
-        byte[] bytes = BitConverter.GetBytes(_id);
-        fixed (byte* pbytes = bytes)
-        {
-            Buffer.MemoryCopy(pbytes, &rv, sizeof(Rid), bytes.Length);
-        }
-        return rv;
+        ReadOnlySpan<ulong> uspan = new(in _id);
+        ReadOnlySpan<byte> bytes = MemoryMarshal.Cast<ulong, byte>(uspan);
+        return MemoryMarshal.Read<Rid>(bytes);
     }
 
-    [Benchmark]
-    public unsafe Rid ConstructRid_Unsafe_Direct()
+    [Benchmark(Baseline = true)]
+    public unsafe Rid ConstructRid_Unsafe_DirectCopy()
     {
         Rid rv;
         fixed (ulong* p = &_id)