Added 16-bit ADD handlers for r/m16, imm16 and r/m16, imm8 instructions

X86Disassembler/X86/Handlers/Add/AddImmToRm16Handler.cs

@@ -0,0 +1,83 @@
+using X86Disassembler.X86.Operands;
+
+namespace X86Disassembler.X86.Handlers.Add;
+
+/// <summary>
+/// Handler for ADD r/m16, imm16 instruction (opcode 81 /0 with 0x66 prefix)
+/// </summary>
+public class AddImmToRm16Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the AddImmToRm16Handler class
+    /// </summary>
+    /// <param name="decoder">The instruction decoder that owns this handler</param>
+    public AddImmToRm16Handler(InstructionDecoder decoder) 
+        : base(decoder)
+    {
+    }
+
+    /// <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)
+    {
+        // ADD r/m16, imm16 is encoded as 0x81 with 0x66 prefix
+        if (opcode != 0x81)
+        {
+            return false;
+        }
+
+        // Only handle when the operand size prefix is present
+        if (!Decoder.HasOperandSizePrefix())
+            return false;
+            
+        // Check if the reg field of the ModR/M byte is 0 (ADD)
+        if (!Decoder.CanReadByte())
+            return false;
+
+        var reg = ModRMDecoder.PeakModRMReg();
+
+        return reg == 0; // 0 = ADD
+    }
+
+    /// <summary>
+    /// Decodes a ADD 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 instruction type
+        instruction.Type = InstructionType.Add;
+
+        // Check if we can read the ModR/M byte
+        if (!Decoder.CanReadByte())
+        {
+            return false;
+        }
+
+        // Read the ModR/M byte
+        var (_, _, _, destOperand) = ModRMDecoder.ReadModRM16();
+
+        // Check if we have enough bytes for the immediate value
+        if (!Decoder.CanReadUShort())
+        {
+            return false;
+        }
+
+        // Read the immediate value
+        ushort imm16 = Decoder.ReadUInt16();
+
+        // Set the structured operands
+        instruction.StructuredOperands = 
+        [
+            destOperand,
+            OperandFactory.CreateImmediateOperand(imm16)
+        ];
+
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/Add/AddImmToRm16SignExtendedHandler.cs

@@ -0,0 +1,85 @@
+using X86Disassembler.X86.Operands;
+
+namespace X86Disassembler.X86.Handlers.Add;
+
+/// <summary>
+/// Handler for ADD r/m16, imm8 instruction (opcode 83 /0 with 0x66 prefix)
+/// </summary>
+public class AddImmToRm16SignExtendedHandler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the AddImmToRm16SignExtendedHandler class
+    /// </summary>
+    /// <param name="decoder">The instruction decoder that owns this handler</param>
+    public AddImmToRm16SignExtendedHandler(InstructionDecoder decoder) 
+        : base(decoder)
+    {
+    }
+
+    /// <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)
+    {
+        // ADD r/m16, imm8 is encoded as 0x83 with 0x66 prefix
+        if (opcode != 0x83)
+        {
+            return false;
+        }
+
+        // Only handle when the operand size prefix is present
+        if (!Decoder.HasOperandSizePrefix())
+            return false;
+            
+        // Check if the reg field of the ModR/M byte is 0 (ADD)
+        if (!Decoder.CanReadByte())
+            return false;
+
+        var reg = ModRMDecoder.PeakModRMReg();
+
+        return reg == 0; // 0 = ADD
+    }
+
+    /// <summary>
+    /// Decodes a ADD r/m16, 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 instruction type
+        instruction.Type = InstructionType.Add;
+
+        // Check if we can read the ModR/M byte
+        if (!Decoder.CanReadByte())
+        {
+            return false;
+        }
+
+        // Read the ModR/M byte
+        var (_, _, _, destOperand) = ModRMDecoder.ReadModRM16();
+
+        // Check if we have enough bytes for the immediate value
+        if (!Decoder.CanRead(1))
+        {
+            return false;
+        }
+
+        // Read the immediate value (sign-extended from 8-bit to 16-bit)
+        sbyte imm8 = (sbyte)Decoder.ReadByte();
+        short signExtendedImm = imm8;
+        uint immValue = (ushort)signExtendedImm; // Convert to uint for the operand factory
+
+        // Set the structured operands
+        instruction.StructuredOperands = 
+        [
+            destOperand,
+            OperandFactory.CreateImmediateOperand(immValue)
+        ];
+
+        return true;
+    }
+}