sorry for my bad english. today i download RetroArch Android releases (v0.9.9.2 - r16) .MAME2003 efficiency is higher than 0.39.But in fact I only need this function,if i wants to change game,i will open so many folders.so ,anyone can upload MAME2003 only? my moble phone model is SONY Xperia PLAY R800i,the layout button design is not human.?D ,In this respect Mame4droid Reloaded is better, anyone can show me how to change the Settings?
If you only want MAME, you can delete the other libraries. They should be located in /data/data/org.retroarch/lib/ (requires root).
thank you very much 
If you’re not rooted I found that this works:
- Download the RetroArch apk from this website
- Open it (but do not extract) with an archive editor like 7-zip
- Delete the cores you don’t want from libs folder
- Install the apk
Don’t delete libretro-activity.so. If you have an ARM device you can safely remove the x86 and MIPS folders to save a lot of space.
awesome! thank you!