ParkanPlayground/X86Disassembler/X86/Handlers/Or/OrRm32R32Handler.cs

namespace X86Disassembler.X86.Handlers.Or;

using Operands;

/// <summary>
/// Handler for OR r/m32, r32 instruction (0x09)
/// </summary>
public class OrRm32R32Handler : InstructionHandler
{
    /// <summary>
    /// Initializes a new instance of the OrRm32R32Handler class
    /// </summary>
    /// <param name="decoder">The instruction decoder that owns this handler</param>
    public OrRm32R32Handler(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)
    {
        // Only handle opcode 0x09 when the operand size prefix is NOT present
        // This ensures 16-bit handlers get priority when the prefix is present
        return opcode == 0x09 && !Decoder.HasOperandSizePrefix();
    }

    /// <summary>
    /// Decodes an OR r/m32, 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)
    {
        // Set the instruction type
        instruction.Type = InstructionType.Or;
        
        if (!Decoder.CanReadByte())
        {
            return false;
        }

        // Read the ModR/M byte
        // For OR r/m32, r32 (opcode 09):
        // - The r/m field (with mod) specifies the destination operand
        // - The reg field specifies the source operand
        var (mod, reg, rm, destOperand) = ModRMDecoder.ReadModRM();

        // Create the register operand for the reg field
        var regOperand = OperandFactory.CreateRegisterOperand(reg);
        
        // Set the structured operands based on addressing mode
        if (mod == 3) // Direct register addressing
        {
            // Create the register operand for the r/m field
            var rmOperand = OperandFactory.CreateRegisterOperand(rm);
            
            // Set the structured operands
            instruction.StructuredOperands = 
            [
                rmOperand,  // Destination is r/m
                regOperand  // Source is reg
            ];
        }
        else // Memory addressing
        {
            // Set the structured operands
            instruction.StructuredOperands = 
            [
                destOperand, // Destination is r/m (memory)
                regOperand   // Source is reg
            ];
        }

        return true;
    }
}