Ts_rank internals

Hi,

I tried to understand how ts_rank works, but I failed. What does Cover
function do? How does it work? What is the DocRepresentation data
structure like? I can see the definition of the struct, and the
get_docrep function to convert to that format, but by reading those I
can't figure out what the resulting DocRepresentation looks like.

I wonder if we could get rid of the istrue flag in QueryOperand, and use
a local BitmapSet variable instead? It seems wrong to have a temporary
flag that's only used in one function, in a struct that's used everywhere.

--  Heikki Linnakangas EnterpriseDB   http://www.enterprisedb.com