details about HTTP/2 Huffman

[tokers]

Hello!

I am wondering some details about HTTP/2 Huffman.

There is a statement (
http://hg.nginx.org/nginx/file/tip/src/http/v2/ngx_http_v2_huff_encode.c#l238
)

buf |= (ngx_uint_t) –1 >> pending;

I am confused about this statement, why should we set the low bits of but
to 1 (sizeof(buf) - pending).

On the other hand, i am interested in the the generation about the huffman
decode table (
http://hg.nginx.org/nginx/file/tip/src/http/v2/ngx_http_v2_huff_decode.c#l25
),

is this really a Huffman tree, which takes 4bits each time?
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