Fixed floating point instruction handling. Removed redundant FNSTSW AX check from FloatingPointHandler and added dedicated test for FnstswHandler.

X86Disassembler/X86/Handlers/Test/TestRegMem8Handler.cs

@@ -0,0 +1,98 @@
+namespace X86Disassembler.X86.Handlers.Test;
+
+/// <summary>
+/// Handler for TEST r/m8, r8 instruction (0x84)
+/// </summary>
+public class TestRegMem8Handler : InstructionHandler
+{
+    // ModR/M decoder
+    private readonly ModRMDecoder _modRMDecoder;
+    
+    /// <summary>
+    /// Initializes a new instance of the TestRegMem8Handler 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 TestRegMem8Handler(byte[] codeBuffer, InstructionDecoder decoder, int length) 
+        : base(codeBuffer, decoder, length)
+    {
+        _modRMDecoder = new ModRMDecoder(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 == 0x84;
+    }
+    
+    /// <summary>
+    /// Decodes a TEST 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 = "test";
+        
+        int position = Decoder.GetPosition();
+        
+        if (position >= Length)
+        {
+            return false;
+        }
+        
+        // Read the ModR/M byte
+        byte modRM = CodeBuffer[position++];
+        Decoder.SetPosition(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);
+        
+        // For direct register addressing (mod == 3), the r/m field specifies a register
+        if (mod == 3)
+        {
+            // Get the register names
+            string rmReg = GetRegister8(rm);
+            string regReg = GetRegister8(reg);
+            
+            // Set the operands (TEST r/m8, r8)
+            // In x86 assembly, the TEST instruction has the operand order r/m8, r8
+            // According to Ghidra and standard x86 assembly convention, it should be TEST CL,AL
+            // where CL is the r/m operand and AL is the reg operand
+            instruction.Operands = $"{rmReg}, {regReg}";
+        }
+        else
+        {
+            // Decode the memory operand
+            string memOperand = _modRMDecoder.DecodeModRM(mod, rm, true);
+            
+            // Get the register name
+            string regReg = GetRegister8(reg);
+            
+            // Set the operands (TEST r/m8, r8)
+            instruction.Operands = $"{memOperand}, {regReg}";
+        }
+        
+        return true;
+    }
+    
+    /// <summary>
+    /// Gets the 8-bit register name for the given register index
+    /// </summary>
+    /// <param name="reg">The register index</param>
+    /// <returns>The register name</returns>
+    private static string GetRegister8(byte reg)
+    {
+        string[] registerNames = { "al", "cl", "dl", "bl", "ah", "ch", "dh", "bh" };
+        return registerNames[reg & 0x07];
+    }
+}