Refactor SUB handlers

X86Disassembler/X86/Handlers/Sub/SubImmFromRm8Handler.cs

@@ -0,0 +1,80 @@
+namespace X86Disassembler.X86.Handlers.Sub;
+
+/// <summary>
+/// Handler for SUB r/m8, imm8 instruction (0x80 /5)
+/// </summary>
+public class SubImmFromRm8Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the SubImmFromRm8Handler 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 SubImmFromRm8Handler(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 5 (SUB)
+        int position = Decoder.GetPosition();
+        if (position >= Length)
+            return false;
+
+        byte modRM = CodeBuffer[position];
+        byte reg = (byte) ((modRM & 0x38) >> 3);
+
+        return reg == 5; // 5 = SUB
+    }
+
+    /// <summary>
+    /// Decodes a SUB 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 = "sub";
+
+        // Extract the fields from the ModR/M byte
+        var (mod, reg, rm, operand) = ModRMDecoder.ReadModRM();
+
+        // Read the immediate byte
+        var position = Decoder.GetPosition();
+        if (position >= Length)
+        {
+            return false;
+        }
+
+        byte imm8 = CodeBuffer[position++];
+        Decoder.SetPosition(position);
+
+        // Set the instruction information
+        // For mod == 3, the operand is a register
+        if (mod == 3)
+        {
+            string rmRegName = ModRMDecoder.GetRegisterName(rm, 8);
+            instruction.Operands = $"{rmRegName}, 0x{imm8:X2}";
+        }
+        else // Memory operand
+        {
+            // Get the memory operand string
+            string memOperand = ModRMDecoder.DecodeModRM(mod, rm, false);
+            instruction.Operands = $"byte ptr {memOperand}, 0x{imm8:X2}";
+        }
+
+        return true;
+    }
+}