Add: os.difftime

src/Lua/Standard/OpenLibExtensions.cs

@@ -87,6 +87,7 @@ public static class OpenLibExtensions
 
     static readonly LuaFunction[] osFunctions = [
         ClockFunction.Instance,
+        DiffTimeFunction.Instance,
         ExitFunction.Instance,
         GetEnvFunction.Instance,
         SetLocaleFunction.Instance,

src/Lua/Standard/OperatingSystem/DiffTimeFunction.cs

@@ -0,0 +1,18 @@
+
+using System.Diagnostics;
+
+namespace Lua.Standard.OperatingSystem;
+
+public sealed class DiffTimeFunction : LuaFunction
+{
+    public override string Name => "difftime";
+    public static readonly DiffTimeFunction Instance = new();
+
+    protected override ValueTask<int> InvokeAsyncCore(LuaFunctionExecutionContext context, Memory<LuaValue> buffer, CancellationToken cancellationToken)
+    {
+        var t2 = context.GetArgument<double>(0);
+        var t1 = context.GetArgument<double>(1);
+        buffer.Span[0] = t2 - t1;
+        return new(1);
+    }
+}