Added support for DEC r32 instructions (0x48-0x4F) with tests

X86Disassembler/X86/Handlers/Dec/DecRegHandler.cs

@@ -0,0 +1,49 @@
+namespace X86Disassembler.X86.Handlers.Dec;
+
+/// <summary>
+/// Handler for DEC r32 instructions (0x48-0x4F)
+/// </summary>
+public class DecRegHandler : InstructionHandler
+{
+    /// <summary>
+    /// Initializes a new instance of the DecRegHandler 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 DecRegHandler(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)
+    {
+        // DEC EAX = 0x48, DEC ECX = 0x49, ..., DEC EDI = 0x4F
+        return opcode >= 0x48 && opcode <= 0x4F;
+    }
+
+    /// <summary>
+    /// Decodes a DEC r32 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)
+    {
+        // Calculate the register index (0 for EAX, 1 for ECX, etc.)
+        byte reg = (byte)(opcode - 0x48);
+        
+        // Set the mnemonic
+        instruction.Mnemonic = "dec";
+        
+        // Set the operand (register name)
+        instruction.Operands = GetRegister32(reg);
+        
+        return true;
+    }
+}

X86Disassembler/X86/Handlers/InstructionHandlerFactory.cs

@@ -2,6 +2,7 @@ using X86Disassembler.X86.Handlers.ArithmeticImmediate;
 using X86Disassembler.X86.Handlers.ArithmeticUnary;
 using X86Disassembler.X86.Handlers.Call;
 using X86Disassembler.X86.Handlers.Cmp;
+using X86Disassembler.X86.Handlers.Dec;
 using X86Disassembler.X86.Handlers.FloatingPoint;
 using X86Disassembler.X86.Handlers.Jump;
 using X86Disassembler.X86.Handlers.Lea;
@@ -77,6 +78,9 @@ public class InstructionHandlerFactory
         // Register Cmp handlers
         RegisterCmpHandlers();
         
+        // Register Dec handlers
+        RegisterDecHandlers();
+        
         // Register Data Transfer handlers
         RegisterDataTransferHandlers();
         
@@ -238,6 +242,15 @@ public class InstructionHandlerFactory
         _handlers.Add(new CmpR32Rm32Handler(_codeBuffer, _decoder, _length));
     }
     
+    /// <summary>
+    /// Registers all Dec instruction handlers
+    /// </summary>
+    private void RegisterDecHandlers()
+    {
+        // Add Dec handlers
+        _handlers.Add(new DecRegHandler(_codeBuffer, _decoder, _length));
+    }
+    
     /// <summary>
     /// Registers all Data Transfer instruction handlers
     /// </summary>

X86Disassembler/X86/OpcodeMap.cs

@@ -62,6 +62,16 @@ public static class OpcodeMap
         OneByteOpcodes[0xC6] = "mov"; // MOV r/m8, imm8
         OneByteOpcodes[0xC7] = "mov"; // MOV r/m32, imm32
         
+        // DEC instructions
+        OneByteOpcodes[0x48] = "dec"; // DEC EAX
+        OneByteOpcodes[0x49] = "dec"; // DEC ECX
+        OneByteOpcodes[0x4A] = "dec"; // DEC EDX
+        OneByteOpcodes[0x4B] = "dec"; // DEC EBX
+        OneByteOpcodes[0x4C] = "dec"; // DEC ESP
+        OneByteOpcodes[0x4D] = "dec"; // DEC EBP
+        OneByteOpcodes[0x4E] = "dec"; // DEC ESI
+        OneByteOpcodes[0x4F] = "dec"; // DEC EDI
+        
         // Group 1 instructions (ADD, OR, ADC, SBB, AND, SUB, XOR, CMP)
         OneByteOpcodes[0x80] = "group1b";
         OneByteOpcodes[0x81] = "group1d";

X86DisassemblerTests/DecInstructionTests.cs

@@ -0,0 +1,68 @@
+namespace X86DisassemblerTests;
+
+using System;
+using Xunit;
+using X86Disassembler.X86;
+
+/// <summary>
+/// Tests for DEC instruction handlers
+/// </summary>
+public class DecInstructionTests
+{
+    /// <summary>
+    /// Tests the DEC EAX instruction (0x48)
+    /// </summary>
+    [Fact]
+    public void TestDecEax()
+    {
+        // Arrange
+        byte[] code = { 0x48 }; // DEC EAX
+        
+        // Act
+        Disassembler disassembler = new Disassembler(code, 0x1000);
+        var instructions = disassembler.Disassemble();
+        
+        // Assert
+        Assert.Single(instructions);
+        Assert.Equal("dec", instructions[0].Mnemonic);
+        Assert.Equal("eax", instructions[0].Operands);
+    }
+    
+    /// <summary>
+    /// Tests the DEC ECX instruction (0x49)
+    /// </summary>
+    [Fact]
+    public void TestDecEcx()
+    {
+        // Arrange
+        byte[] code = { 0x49 }; // DEC ECX
+        
+        // Act
+        Disassembler disassembler = new Disassembler(code, 0x1000);
+        var instructions = disassembler.Disassemble();
+        
+        // Assert
+        Assert.Single(instructions);
+        Assert.Equal("dec", instructions[0].Mnemonic);
+        Assert.Equal("ecx", instructions[0].Operands);
+    }
+    
+    /// <summary>
+    /// Tests the DEC EDI instruction (0x4F)
+    /// </summary>
+    [Fact]
+    public void TestDecEdi()
+    {
+        // Arrange
+        byte[] code = { 0x4F }; // DEC EDI
+        
+        // Act
+        Disassembler disassembler = new Disassembler(code, 0x1000);
+        var instructions = disassembler.Disassemble();
+        
+        // Assert
+        Assert.Single(instructions);
+        Assert.Equal("dec", instructions[0].Mnemonic);
+        Assert.Equal("edi", instructions[0].Operands);
+    }
+}