[x265] question about interp

[dave]

For the interpolation primitives there are multiple versions, pp, ps, 
sp, and ss.  Each one adding an offset before a shift.  Yet as I review 
the interpolation section 8.5.3.3.3 of the h265 spec, I don't see where 
an offset is added.  Am I missing something?  Or perhaps the offset 
helps decision making?

thanks,
Dave