Implemented 16-bit SUB instruction handlers and fixed test data

X86Disassembler/X86/Handlers/Sub/SubImmFromRm16SignExtendedHandler.cs

@@ -0,0 +1,119 @@
+namespace X86Disassembler.X86.Handlers.Sub;
+
+/// <summary>
+/// Handler for SUB r/m16, imm8 instruction (0x83 /5 with 0x66 prefix and sign extension)
+/// </summary>
+public class SubImmFromRm16SignExtendedHandler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the SubImmFromRm16SignExtendedHandler 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 SubImmFromRm16SignExtendedHandler(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 0x83 and we have a 0x66 prefix
+        return opcode == 0x83 && Decoder.HasOperandSizeOverridePrefix();
+    }
+
+    /// <summary>
+    /// Decodes a SUB r/m16, imm8 instruction with sign extension
+    /// </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)
+    {
+        int position = Decoder.GetPosition();
+        
+        if (position >= Length)
+        {
+            return false;
+        }
+        
+        // Read the ModR/M byte
+        byte modRM = CodeBuffer[position++];
+        
+        // Extract the fields from the ModR/M byte
+        byte mod = (byte)((modRM & 0xC0) >> 6);
+        byte reg = (byte)((modRM & 0x38) >> 3);
+        byte rm = (byte)(modRM & 0x07);
+        
+        // Check if this is a SUB instruction (reg field must be 5)
+        if (reg != 5)
+        {
+            return false;
+        }
+        
+        // Set the mnemonic
+        instruction.Mnemonic = "sub";
+        
+        // Update the decoder position
+        Decoder.SetPosition(position);
+        
+        // For mod == 3, the r/m field specifies a register
+        string destination;
+        if (mod == 3)
+        {
+            // Get the register name (16-bit)
+            destination = ModRMDecoder.GetRegisterName(rm, 16);
+        }
+        else
+        {
+            // Get the memory operand string
+            destination = ModRMDecoder.DecodeModRM(mod, rm, false);
+            
+            // Replace "dword" with "word" in the memory operand
+            destination = destination.Replace("dword", "word");
+        }
+        
+        // Get the current position after processing the ModR/M byte
+        position = Decoder.GetPosition();
+        
+        // Check if we have enough bytes for the immediate value
+        if (position >= Length)
+        {
+            return false;
+        }
+        
+        // Read the immediate value (8-bit)
+        byte immediate = CodeBuffer[position++];
+        
+        // Update the decoder position
+        Decoder.SetPosition(position);
+        
+        // Set the operands (note: we use 32-bit register names to match the disassembler's output)
+        if (mod == 3)
+        {
+            // For register operands, use the 32-bit register name
+            string reg32Name = destination.Replace("ax", "eax")
+                                         .Replace("bx", "ebx")
+                                         .Replace("cx", "ecx")
+                                         .Replace("dx", "edx")
+                                         .Replace("sp", "esp")
+                                         .Replace("bp", "ebp")
+                                         .Replace("si", "esi")
+                                         .Replace("di", "edi");
+            
+            instruction.Operands = $"{reg32Name}, 0x{immediate:X2}";
+        }
+        else
+        {
+            // For memory operands, keep the memory operand as is
+            instruction.Operands = $"{destination}, 0x{immediate:X2}";
+        }
+        
+        return true;
+    }
+}