Reorganize floating point handlers into logical subfolders

X86Disassembler/X86/Handlers/FloatingPoint/LoadStore/FstpFloat64Handler.cs

@@ -0,0 +1,83 @@
+namespace X86Disassembler.X86.Handlers.FloatingPoint.LoadStore;
+
+using X86Disassembler.X86.Operands;
+
+/// <summary>
+/// Handler for FSTP float64 instruction (DD /3)
+/// </summary>
+public class FstpFloat64Handler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the FstpFloat64Handler class
+    /// </summary>
+    /// <param name="decoder">The instruction decoder that owns this handler</param>
+    public FstpFloat64Handler(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)
+    {
+        // FSTP is DD /3
+        if (opcode != 0xDD) return false;
+
+        if (!Decoder.CanReadByte())
+        {
+            return false;
+        }
+
+        // Check if the ModR/M byte has reg field = 3
+        byte modRm = Decoder.PeakByte();
+        byte reg = (byte)((modRm >> 3) & 0x7);
+        
+        return reg == 3;
+    }
+    
+    /// <summary>
+    /// Decodes a FSTP float64 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 using the specialized FPU method
+        var (mod, reg, fpuRm, rawOperand) = ModRMDecoder.ReadModRMFpu();
+        
+        // Set the instruction type
+        instruction.Type = InstructionType.Fstp;
+
+        // Handle based on addressing mode
+        if (mod != 3) // Memory operand
+        {
+            // Set the structured operands - the operand already has the correct size from ReadModRM
+            instruction.StructuredOperands = 
+            [
+                rawOperand
+            ];
+        }
+        else // Register operand (ST(i))
+        {
+            // For register operands with mod=3, this is FSTP ST(i)
+            var stiOperand = OperandFactory.CreateFPURegisterOperand(fpuRm); // ST(i)
+            
+            // Set the structured operands
+            instruction.StructuredOperands = 
+            [
+                stiOperand
+            ];
+        }
+
+        return true;
+    }
+}