Vorbis dev - Dec 2005 - question about the specification in 7.2.2.1

hello to  vorbis developers,

i am in progress of writing a mini ogg-vorbis decoder, which should work
on the windows ce based smartphone later. 

because i don't need all functionality of libvorbis, I decided to try
writing an own decoder without linking the libs.

so far it went pretty fine, but now there is a problem I cannot solve
with the given information of the specification and the example
implementation.

When it comes to packet decode for floor_type_1 (chapter 7.2.2.1), the
specification said in line 12):

"cval = read from packet using codebook number (vector
[floor1_class_master_book] element [class]) in scalar context" 

well, from that I have understand so far, the codebook number specified
with the (masterbook [class] ) is just a codebook, which I have already
decoded in the setup part.

I am not really sure about this, but when I should read from the packet,
I need at least an information how many bits I should read now. So I
would like to ask which entry of the selected codebook (
masterbook[class] ) should I access to get the length information? 

the same thing in line 17)

(book) should be just a codebook number, but I need an access to the
length information of the codebook. so again, which entry of the
codebook is meant here? 

I would really appreciate it, if somebody could explain the main idea
behind this stuff. 

regards,
Rico