Refactored floating point handlers into specialized classes for better organization and maintainability

X86Disassembler/X86/Handlers/FloatingPoint/Control/FxchHandler.cs

@@ -0,0 +1,87 @@
+namespace X86Disassembler.X86.Handlers.FloatingPoint.Control;
+
+using X86Disassembler.X86.Operands;
+
+/// <summary>
+/// Handler for FXCH instruction (D9 /1 with mod=3)
+/// </summary>
+public class FxchHandler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the FxchHandler class
+    /// </summary>
+    /// <param name="decoder">The instruction decoder that owns this handler</param>
+    public FxchHandler(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)
+    {
+        // FXCH is D9 /1 with mod=3
+        if (opcode != 0xD9) return false;
+
+        if (!Decoder.CanReadByte())
+        {
+            return false;
+        }
+
+        // Check if the ModR/M byte has reg field = 1 and mod = 3
+        byte modRm = Decoder.PeakByte();
+        byte reg = (byte)((modRm >> 3) & 0x7);
+        byte mod = (byte)((modRm >> 6) & 0x3);
+        
+        // Only handle register operands (mod = 3) with reg = 1
+        return reg == 1 && mod == 3;
+    }
+    
+    /// <summary>
+    /// Decodes a FXCH 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)
+    {
+        if (!Decoder.CanReadByte())
+        {
+            return false;
+        }
+
+        // Read the ModR/M byte
+        var (mod, reg, rm, _) = ModRMDecoder.ReadModRM();
+        
+        // Set the instruction type
+        instruction.Type = InstructionType.Fxch;
+
+        // Map rm field to FPU register index
+        FpuRegisterIndex stIndex = rm switch
+        {
+            RegisterIndex.A => FpuRegisterIndex.ST0,
+            RegisterIndex.C => FpuRegisterIndex.ST1,
+            RegisterIndex.D => FpuRegisterIndex.ST2,
+            RegisterIndex.B => FpuRegisterIndex.ST3,
+            RegisterIndex.Sp => FpuRegisterIndex.ST4,
+            RegisterIndex.Bp => FpuRegisterIndex.ST5,
+            RegisterIndex.Si => FpuRegisterIndex.ST6,
+            RegisterIndex.Di => FpuRegisterIndex.ST7,
+            _ => FpuRegisterIndex.ST0 // Default case, should not happen
+        };
+        
+        // Create the FPU register operand
+        var operand = OperandFactory.CreateFPURegisterOperand(stIndex);
+        
+        // Set the structured operands
+        instruction.StructuredOperands = 
+        [
+            operand
+        ];
+
+        return true;
+    }
+}