Fixed FnstswHandler test by registering the handler in InstructionHandlerFactory

X86Disassembler/X86/Handlers/Xchg/XchgEaxRegHandler.cs

@@ -0,0 +1,57 @@
+namespace X86Disassembler.X86.Handlers.Xchg;
+
+/// <summary>
+/// Handler for XCHG EAX, r32 instruction (0x90-0x97)
+/// </summary>
+public class XchgEaxRegHandler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XchgEaxRegHandler class
+    /// </summary>
+    /// <param name="codeBuffer">The buffer containing the code to decode</param>
+    /// <param name="decoder">The instruction decoder that owns this handler</param>
+    /// <param name="length">The length of the buffer</param>
+    public XchgEaxRegHandler(byte[] codeBuffer, InstructionDecoder decoder, int length) 
+        : base(codeBuffer, decoder, length)
+    {
+    }
+    
+    /// <summary>
+    /// Checks if this handler can decode the given opcode
+    /// </summary>
+    /// <param name="opcode">The opcode to check</param>
+    /// <returns>True if this handler can decode the opcode</returns>
+    public override bool CanHandle(byte opcode)
+    {
+        return opcode >= 0x90 && opcode <= 0x97;
+    }
+    
+    /// <summary>
+    /// Decodes an XCHG EAX, r32 instruction
+    /// </summary>
+    /// <param name="opcode">The opcode of the instruction</param>
+    /// <param name="instruction">The instruction object to populate</param>
+    /// <returns>True if the instruction was successfully decoded</returns>
+    public override bool Decode(byte opcode, Instruction instruction)
+    {
+        // Special case for NOP (XCHG EAX, EAX)
+        if (opcode == 0x90)
+        {
+            instruction.Mnemonic = "nop";
+            instruction.Operands = "";
+            return true;
+        }
+        
+        // Set the mnemonic
+        instruction.Mnemonic = "xchg";
+        
+        // Register is encoded in the low 3 bits of the opcode
+        int reg = opcode & 0x07;
+        string regName = ModRMDecoder.GetRegisterName(reg, 32);
+        
+        // Set the operands
+        instruction.Operands = $"eax, {regName}";
+        
+        return true;
+    }
+}