Oracle's automatic extent allocation (next extent) size algorithm - anyone?

For Oracle segments in Locally Managed Tablespaces with *AUTOMATIC* extent allocation (instead of UNIFORM extent allocation) , does anyone have the algorithm that Oracle uses to determine the next extent size that is based on the size of the segment?

I used to have it where it went something like:

IF segment > xG , then next extent = xGB IF Segment > xMB then next extent = xMB

I'm trying to find it but can't quickly locate it (because I'm not sure what keywords to search for)