what is the hash function ' s main idea in tsearch2?

Teodor Sigaev :
thanks for your help.
And now i' m wondering such a question : how is the signatures in the tsearch2 signature tree are made,because the hash function crc32_sz() is too complex for me to read.what's the hash func 's basic idea ?There are so many tsvectors in the db abd crc32_sz() used what feathers done such a difficult job,will you give a short descripton?

thanks