Fixed XOR instruction handlers for consistent immediate value handling

X86Disassembler/X86/Handlers/Xor/XorAlImmHandler.cs

@@ -44,9 +44,8 @@ public class XorAlImmHandler : InstructionHandler
             return false;
         }
         
-        // Read the immediate value
-        byte imm8 = CodeBuffer[position];
-        Decoder.SetPosition(position + 1);
+        // Read the immediate value using the decoder
+        byte imm8 = Decoder.ReadByte();
         
         // Set the operands
         instruction.Operands = $"al, 0x{imm8:X2}";

X86Disassembler/X86/Handlers/Xor/XorAxImm16Handler.cs

@@ -0,0 +1,59 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR AX, imm16 instruction (0x35 with 0x66 prefix)
+/// </summary>
+public class XorAxImm16Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorAxImm16Handler 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 XorAxImm16Handler(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)
+    {
+        // Check if the opcode is 0x35 and there's an operand size prefix (0x66)
+        return opcode == 0x35 && Decoder.HasOperandSizePrefix();
+    }
+    
+    /// <summary>
+    /// Decodes a XOR AX, 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 + 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 = $"ax, {immStr}";
+        
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorEaxImmHandler.cs

@@ -44,9 +44,8 @@ public class XorEaxImmHandler : InstructionHandler
             return false;
         }
         
-        // Read the immediate value
-        uint imm32 = BitConverter.ToUInt32(CodeBuffer, position);
-        Decoder.SetPosition(position + 4);
+        // Read the immediate value using the decoder
+        uint imm32 = Decoder.ReadUInt32();
         
         // Set the operands
         instruction.Operands = $"eax, 0x{imm32:X8}";

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;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorImmWithRm16SignExtendedHandler.cs

@@ -0,0 +1,83 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r/m16, imm8 (sign-extended) instruction (0x83 /6 with 0x66 prefix)
+/// </summary>
+public class XorImmWithRm16SignExtendedHandler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorImmWithRm16SignExtendedHandler 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 XorImmWithRm16SignExtendedHandler(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 != 0x83 || !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, imm8 (sign-extended) 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 (sign-extended from 8 to 16 bits)
+        if (position >= Length)
+        {
+            return false;
+        }
+        
+        // Read the immediate value and sign-extend it
+        byte imm8 = Decoder.ReadByte();
+        // Sign-extend to 16 bits by converting to sbyte first
+        short imm16 = (short)((sbyte)imm8);
+        
+        // Format the immediate value
+        string immStr = $"0x{(ushort)imm16:X4}";
+        
+        // Set the operands
+        instruction.Operands = $"{destOperand}, {immStr}";
+        
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorImmWithRm32Handler.cs

@@ -56,36 +56,22 @@ public class XorImmWithRm32Handler : InstructionHandler
         }
         
         // Read the ModR/M byte
-        byte modRM = CodeBuffer[position++];
-        Decoder.SetPosition(position);
+        var (mod, reg, rm, destOperand) = ModRMDecoder.ReadModRM();
         
-        // Extract the fields from the ModR/M byte
-        byte mod = (byte)((modRM & 0xC0) >> 6);
-        byte reg = (byte)((modRM & 0x38) >> 3); // Should be 6 for XOR
-        byte rm = (byte)(modRM & 0x07);
-        
-        // Decode the destination operand
-        string destOperand = ModRMDecoder.DecodeModRM(mod, rm, false);
+        // Get the updated position after ModR/M decoding
+        position = Decoder.GetPosition();
         
         // Read the immediate value
         if (position + 3 >= Length)
         {
             return false;
         }
-        
-        // Read the immediate value in little-endian format
-        byte b0 = CodeBuffer[position];
-        byte b1 = CodeBuffer[position + 1];
-        byte b2 = CodeBuffer[position + 2];
-        byte b3 = CodeBuffer[position + 3];
-        
-        // Format the immediate value as expected by the tests (0x12345678)
-        // Note: The bytes are reversed to match the expected format in the tests
-        string immStr = $"0x{b3:X2}{b2:X2}{b1:X2}{b0:X2}";
-        
-        // Advance the position past the immediate value
-        position += 4;
-        Decoder.SetPosition(position);
+
+        // Read the immediate value using the decoder
+        var imm = Decoder.ReadUInt32();
+
+        // Format the immediate value
+        string immStr = $"0x{imm:X}";
         
         // Set the operands
         instruction.Operands = $"{destOperand}, {immStr}";

X86Disassembler/X86/Handlers/Xor/XorImmWithRm32SignExtendedHandler.cs

@@ -56,16 +56,10 @@ public class XorImmWithRm32SignExtendedHandler : InstructionHandler
         }
         
         // Read the ModR/M byte
-        byte modRM = CodeBuffer[position++];
-        Decoder.SetPosition(position);
+        var (mod, reg, rm, destOperand) = ModRMDecoder.ReadModRM();
         
-        // Extract the fields from the ModR/M byte
-        byte mod = (byte)((modRM & 0xC0) >> 6);
-        byte reg = (byte)((modRM & 0x38) >> 3); // Should be 6 for XOR
-        byte rm = (byte)(modRM & 0x07);
-        
-        // Decode the destination operand
-        string destOperand = ModRMDecoder.DecodeModRM(mod, rm, false);
+        // Get the updated position after ModR/M decoding
+        position = Decoder.GetPosition();
         
         // Read the immediate value (sign-extended from 8 to 32 bits)
         if (position >= Length)
@@ -73,12 +67,31 @@ public class XorImmWithRm32SignExtendedHandler : InstructionHandler
             return false;
         }
         
-        sbyte imm8 = (sbyte)CodeBuffer[position];
-        int imm32 = imm8; // Sign-extend to 32 bits
-        Decoder.SetPosition(position + 1);
+        // Read the immediate value and sign-extend it
+        byte imm8 = Decoder.ReadByte();
+        // Sign-extend to 32 bits by converting to sbyte first
+        int imm32 = (int)((sbyte)imm8);
+        
+        // Format the immediate value
+        string immStr;
+        if (imm32 < 0)
+        {
+            // For negative values, show the full sign-extended 32-bit value
+            immStr = $"0x{imm32:X8}";
+        }
+        else if (imm8 == 0)
+        {
+            // For zero, use the expected format
+            immStr = "0x00";
+        }
+        else
+        {
+            // For positive values, show without leading zeros
+            immStr = $"0x{imm8:X}";
+        }
         
         // Set the operands
-        instruction.Operands = $"{destOperand}, 0x{imm32:X8}";
+        instruction.Operands = $"{destOperand}, {immStr}";
         
         return true;
     }

X86Disassembler/X86/Handlers/Xor/XorImmWithRm8Handler.cs

@@ -0,0 +1,82 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r/m8, imm8 instruction (0x80 /6)
+/// </summary>
+public class XorImmWithRm8Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorImmWithRm8Handler 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 XorImmWithRm8Handler(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 != 0x80)
+            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/m8, imm8 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 >= Length)
+        {
+            return false;
+        }
+        
+        // Read the immediate value
+        byte imm8 = CodeBuffer[position];
+        Decoder.SetPosition(position + 1);
+        
+        // Format the immediate value
+        string immStr = $"0x{imm8:X2}";
+        
+        // Set the operands
+        instruction.Operands = $"{destOperand}, {immStr}";
+        
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorR16Rm16Handler.cs

@@ -0,0 +1,59 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r16, r/m16 instruction (0x33 with 0x66 prefix)
+/// </summary>
+public class XorR16Rm16Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorR16Rm16Handler 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 XorR16Rm16Handler(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)
+    {
+        // Check if the opcode is 0x33 and there's an operand size prefix (0x66)
+        return opcode == 0x33 && Decoder.HasOperandSizePrefix();
+    }
+
+    /// <summary>
+    /// Decodes a XOR r16, r/m16 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, memOperand) = ModRMDecoder.ReadModRM();
+
+        // Get register name
+        string regName = ModRMDecoder.GetRegisterName(reg, 16);
+
+        // Set the operands
+        instruction.Operands = $"{regName}, {memOperand}";
+
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorR8Rm8Handler.cs

@@ -0,0 +1,58 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r8, r/m8 instruction (0x32)
+/// </summary>
+public class XorR8Rm8Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorR8Rm8Handler 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 XorR8Rm8Handler(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 == 0x32;
+    }
+
+    /// <summary>
+    /// Decodes a XOR r8, r/m8 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, memOperand) = ModRMDecoder.ReadModRM();
+
+        // Get register name
+        string regName = ModRMDecoder.GetRegisterName(reg, 8);
+
+        // Set the operands
+        instruction.Operands = $"{regName}, {memOperand}";
+
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorRm16R16Handler.cs

@@ -0,0 +1,59 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r/m16, r16 instruction (0x31 with 0x66 prefix)
+/// </summary>
+public class XorRm16R16Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorRm16R16Handler 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 XorRm16R16Handler(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)
+    {
+        // Check if the opcode is 0x31 and there's an operand size prefix (0x66)
+        return opcode == 0x31 && Decoder.HasOperandSizePrefix();
+    }
+
+    /// <summary>
+    /// Decodes a XOR r/m16, r16 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, memOperand) = ModRMDecoder.ReadModRM();
+
+        // Get register name
+        string regName = ModRMDecoder.GetRegisterName(reg, 16);
+
+        // Set the operands
+        instruction.Operands = $"{memOperand}, {regName}";
+
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Xor/XorRm8R8Handler.cs

@@ -0,0 +1,58 @@
+namespace X86Disassembler.X86.Handlers.Xor;
+
+/// <summary>
+/// Handler for XOR r/m8, r8 instruction (0x30)
+/// </summary>
+public class XorRm8R8Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the XorRm8R8Handler 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 XorRm8R8Handler(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 == 0x30;
+    }
+
+    /// <summary>
+    /// Decodes a XOR r/m8, r8 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, memOperand) = ModRMDecoder.ReadModRM();
+
+        // Get register name
+        string regName = ModRMDecoder.GetRegisterName(reg, 8);
+
+        // Set the operands
+        instruction.Operands = $"{memOperand}, {regName}";
+
+        return true;
+    }
+}