Parse XREF table and stream

I open Pdf Reference 1.7 file with a binary viewer program and I want to parse the xref data.

At the end of file is:

startxref

129

%%EOF

At offset 129 is the linearization xref-table with 817 entries and this trailer:

trailer

<</Size 334093 /Prev 25807185 /XRefStm 186352 /Root 333277 0 R/Info 109959 0 R>>

startxref

0

%%EOF

Xref table starts at 25807185 offset and has 333276 entries but more then half of them are free.

XRef stream at 186352 offset and has these data:

334091 0 obj<</Length 3663/Filter/FlateDecode/W[1 2 1]/Index[109960 223316]/DecodeParms<</Columns 4/Predictor 12>>/Size 333276/Type/XRef>> stream.....

1.Can you tell me witch objects are at xref stream and witch at xref table? Are there some entries in both XREFs ?

2.Whith what sequence should i parse the XREFs?  A parser (>1.4) should look only at xref stream?

3. 2 bytes for type 1 objects ( W[1 2 1] ) i dont think are enough for offset position since the file is about 30MB, so how are they recorded.

Thank You.