I'm trying to upload a user photo within a custom module that I am building, but I can't figure out the file structure that I should be using.  Is there a method in the core that I can use to accomplish this task?

When I upload a photo via the profile tool, the image is placed in a folder such as Portals\0\Users\129\85\385

I understand what /Users/ is and /385 is the userid, but I don't know where the /129 and /85 come from.  Does anyone know?