ryujinx/Ryujinx.HLE/HOS/Services/Am/AppletAE/Storage/StorageHelper.cs

using Ryujinx.Common.Memory;
using Ryujinx.HLE.HOS.Services.Account.Acc;
using System.IO;

namespace Ryujinx.HLE.HOS.Services.Am.AppletAE.Storage
{
    class StorageHelper
    {
        private const uint LaunchParamsMagic = 0xc79497ca;

        public static byte[] MakeLaunchParams(UserProfile userProfile)
        {
            // Size needs to be at least 0x88 bytes otherwise application errors.
            using (MemoryStream ms = MemoryStreamManager.Shared.GetStream())
            {
                BinaryWriter writer = new BinaryWriter(ms);

                ms.SetLength(0x88);

                writer.Write(LaunchParamsMagic);
                writer.Write(1);  // IsAccountSelected? Only lower 8 bits actually used.
                userProfile.UserId.Write(writer);

                return ms.ToArray();
            }
        }
    }
}