Fixed XOR instruction handlers for consistent immediate value handling

X86Disassembler/X86/Handlers/Xor/XorImmWithRm16Handler.cs

@@ -0,0 +1,81 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r/m16, imm16 instruction (0x81 /6 with 0x66 prefix)
+/// </summary>
+public class XorImmWithRm16Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorImmWithRm16Handler 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 XorImmWithRm16Handler(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)
+    {
+        if (opcode != 0x81 || !Decoder.HasOperandSizePrefix())
+            return false;
+            
+        // Check if the reg field of the ModR/M byte is 6 (XOR)
+        int position = Decoder.GetPosition();
+        if (position >= Length)
+            return false;
+            
+        byte modRM = CodeBuffer[position];
+        byte reg = (byte)((modRM & 0x38) >> 3);
+        
+        return reg == 6; // 6 = XOR
+    }
+    
+    /// <summary>
+    /// Decodes a XOR r/m16, imm16 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)
+    {
+        // Set the mnemonic
+        instruction.Mnemonic = "xor";
+        
+        int position = Decoder.GetPosition();
+        
+        if (position >= Length)
+        {
+            return false;
+        }
+        
+        // Read the ModR/M byte
+        var (mod, reg, rm, destOperand) = ModRMDecoder.ReadModRM();
+        
+        // Get the updated position after ModR/M decoding
+        position = Decoder.GetPosition();
+        
+        // Read the immediate value
+        if (position + 1 >= Length)
+        {
+            return false;
+        }
+        
+        // Read the immediate value using the decoder
+        ushort imm16 = Decoder.ReadUInt16();
+        
+        // Format the immediate value
+        string immStr = $"0x{imm16:X4}";
+        
+        // Set the operands
+        instruction.Operands = $"{destOperand}, {immStr}";
+        
+        return true;
+    }
+}