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

X86Disassembler/X86/Handlers/FloatingPointHandler.cs

@@ -114,8 +114,8 @@ public class FloatingPointHandler : InstructionHandler
     /// </summary>
     private static void InitializeTwoByteInstructions()
     {
-        // DF E0 - FNSTSW AX (Store FPU status word to AX without checking for pending unmasked floating-point exceptions)
+        // We no longer need to handle FNSTSW AX (DF E0) here since we have a dedicated FnstswHandler
-        TwoByteInstructions.Add(0xDFE0, "fnstsw");
+        // that is registered before this handler in the InstructionHandlerFactory
         
         // Add other two-byte instructions as needed
     }
@@ -166,14 +166,8 @@ public class FloatingPointHandler : InstructionHandler
             if (TwoByteInstructions.TryGetValue(twoByteOpcode, out string? mnemonic) && mnemonic != null)
             {
                 instruction.Mnemonic = mnemonic;
-                
+                Decoder.SetPosition(position + 1); // Skip the second byte
-                // Special handling for specific instructions
+                return true;
-                if (twoByteOpcode == 0xDFE0) // FNSTSW AX
-                {
-                    instruction.Operands = "ax";
-                    Decoder.SetPosition(position + 1); // Skip the second byte
-                    return true;
-                }
             }
         }
         

X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs

@@ -1,3 +1,5 @@
+using X86Disassembler.X86.Handlers.Test;
+
 namespace X86Disassembler.X86.Handlers;
 
 using X86Disassembler.X86.Handlers.Group1;

X86Disassembler/X86/Handlers/Test/TestAlImmHandler.cs

@@ -1,4 +1,4 @@
-namespace X86Disassembler.X86.Handlers;
+namespace X86Disassembler.X86.Handlers.Test;
 
 /// <summary>
 /// Handler for TEST AL, imm8 instruction (0xA8)

X86Disassembler/X86/Handlers/Test/TestEaxImmHandler.cs

@@ -1,4 +1,4 @@
-namespace X86Disassembler.X86.Handlers;
+namespace X86Disassembler.X86.Handlers.Test;
 
 /// <summary>
 /// Handler for TEST EAX, imm32 instruction (0xA9)

X86Disassembler/X86/Handlers/Test/TestRegMem8Handler.cs

@@ -1,4 +1,4 @@
-namespace X86Disassembler.X86.Handlers;
+namespace X86Disassembler.X86.Handlers.Test;
 
 /// <summary>
 /// Handler for TEST r/m8, r8 instruction (0x84)

X86Disassembler/X86/Handlers/Test/TestRegMemHandler.cs

@@ -1,4 +1,4 @@
-namespace X86Disassembler.X86.Handlers;
+namespace X86Disassembler.X86.Handlers.Test;
 
 /// <summary>
 /// Handler for TEST r/m32, r32 instruction (0x85)

X86DisassemblerTests/FloatingPointInstructionTests.cs

@@ -0,0 +1,32 @@
+namespace X86DisassemblerTests;
+
+using System;
+using Xunit;
+using X86Disassembler.X86;
+using X86Disassembler.X86.Handlers;
+
+/// <summary>
+/// Tests for floating-point instruction handlers
+/// </summary>
+public class FloatingPointInstructionTests
+{
+    /// <summary>
+    /// Tests the FnstswHandler for decoding FNSTSW AX instruction
+    /// </summary>
+    [Fact]
+    public void FnstswHandler_DecodesFnstswAx_Correctly()
+    {
+        // Arrange
+        // FNSTSW AX (DF E0)
+        byte[] codeBuffer = new byte[] { 0xDF, 0xE0 };
+        var decoder = new InstructionDecoder(codeBuffer, codeBuffer.Length);
+        
+        // Act
+        var instruction = decoder.DecodeInstruction();
+        
+        // Assert
+        Assert.NotNull(instruction);
+        Assert.Equal("fnstsw", instruction.Mnemonic);
+        Assert.Equal("ax", instruction.Operands);
+    }
+}