I try the putty fork, its seems fialed to uncompress it own compressed data. Perhaps its compressed data is malformed.
I also look at the trees.c of the the official zlib. I do not understand the code, too complex for me. AFAICU it does not generate huffman codes using any standard algorithm, but it assigns bit lengths using some heuristics (trail and error). I guess we can try using hcodes to get an initial guess of bit lengths and then iterate to make it satisfy the 2 rules. Чт, 11 сен 2014, bill lam написал(а): > the frequencies (guessing from bit lengths) should be something like 2 3 1 1 > (2 3 1 1) hcodes 'ABCD' > > the hard part is the inverse problem: how to get the huffman code with > prior knowing the bits for each symbol. Your pointer to the putty > fork looks like helpful. The comment is in lines 861 to 914, the code > itself in line 915 to 964. Do you know how to express it in J? > Thanks. > > On Thu, Sep 11, 2014 at 2:57 PM, Joe Bogner <[email protected]> wrote: > > Here a few other links ... after reading through the RFC. Not sure if > > they help, but just sharing from my own research into assisting on > > this topic > > > > https://github.com/evegard/pngview/blob/master/huffman.c#L54 > > > > And a fork of the putty version with dynamic huffman coding: > > http://rc.quest.com/viewvc/putty/trunk/halibut/deflate.c?diff_format=s&revision=2&view=markup > > > > Or just generally googling some of the code from the RFC: > > https://www.google.com/search?q=next_code%5Blen%5D%2B%2B%3B&oq=next_code%5Blen%5D%2B%2B%3B&aqs=chrome..69i57.387j0j7&sourceid=chrome&es_sm=93&ie=UTF-8#q=next_code%5Blen%5D%2B%2B%3B&start=20 > > > > > > Using the code from > > http://www.jsoftware.com/jwiki/Essays/Huffman%20Coding, I got stuck > > trying to match a simple example to the binary tree in the RFC: > > > > From the RFC: > > > > /\ Symbol Code > > 0 1 ------ ---- > > / \ A 00 > > /\ B B 1 > > 0 1 C 011 > > / \ D 010 > > A /\ > > 0 1 > > / \ > > D C > > > > > > > > (4#1) hcodes 'ABCD' > > ┌───┬───┬───┬───┐ > > │0 0│0 1│1 0│1 1│ > > └───┴───┴───┴───┘ > > > > Per the RFC, ideally that should match this? '00';'1';'011';'010' > > > > > > From there, it seems like a pretty straightforward exercise to > > transliterate the C code from the RFC into J code to recode the > > example to: > > > > > > Symbol Code > > ------ ---- > > A 10 > > B 0 > > C 110 > > D 111 > > > > > > I would probably start with a looping construct like what's in the RFC > > and then figure out a more J way to do it, but first I would need to > > figure out how to create the binary tree in that initial format. > > > > On Wed, Sep 10, 2014 at 7:41 PM, bill lam <[email protected]> wrote: > >> Thanks Joe, > >> putty only use zlib static huffman for encoding so that it does not build > >> any huffman dictionary table. > >> > >> The zlib static huffman code does not care about individual symbol's > >> frequency, it just encode 0 to 286 into bits, see section 3.2.6. > >> On Sep 11, 2014 1:26 AM, "Joe Bogner" <[email protected]> wrote: > >> > >>> You've already likely considered this, but if it were me I would compare > >>> results to a working implementation. The one from putty seems pretty clean > >>> and standalone: > >>> https://raw.githubusercontent.com/grumpydev/PortablePuTTY/master/SSHZLIB.C > >>> . I was able to compile it on windows no problem and I assume it'd be fine > >>> on linux as well. > >>> > >>> On Wed, Sep 10, 2014 at 1:00 PM, Raul Miller <[email protected]> > >>> wrote: > >>> > >>> > I think the use of the term "consecutive" rather than "sequential" is > >>> > telling. > >>> > > >>> > The described algorithm is: compute the huffman code lengths: > >>> > #@>F1 hcodes A1 > >>> > 1 3 7 7 6 6 6 6 6 6 6 2 > >>> > > >>> > Then assign ascending huffman codes first in length order and then > >>> > within codes of the same length. > >>> > > >>> > Taken literally, that might be something like this: > >>> > > >>> > H=: 4 :0 > >>> > L=.#@> x hcodes y > >>> > U=.~.L > >>> > ;<@(({.{.U e.~i.&.<:@{.)<@:+"1-@{.{."1 #:@i.@#)/.~L > >>> > ) > >>> > > >>> > ":@>F1 H A1 > >>> > 0 > >>> > 1 1 0 > >>> > 1 1 1 0 0 1 0 > >>> > 1 1 1 0 0 1 1 > >>> > 1 1 1 0 0 0 > >>> > 1 1 1 0 0 1 > >>> > 1 1 1 0 1 0 > >>> > 1 1 1 0 1 1 > >>> > 1 1 1 1 0 0 > >>> > 1 1 1 1 0 1 > >>> > 1 1 1 1 1 0 > >>> > 1 0 > >>> > > >>> > But is this correct? Is it actually safe to leave the results like > >>> > this - with all codes of the same length being consecutive to each > >>> > other? > >>> > > >>> > F (hcodes -:&:(#@>) H) A > >>> > 0 > >>> > > >>> > No. > >>> > > >>> > So... "consecutive" must refer only to the values used and not their > >>> > order within the result. > >>> > > >>> > Perhaps something like this: > >>> > > >>> > deflatecodes=:4 :0 > >>> > L=.#@> x hcodes y > >>> > U=.~.L > >>> > R=. ;<@(({.{.U e.~i.&.<:@{.)<@:+"1-@{.{."1 #:@i.@#)/.~L > >>> > R/:;(</. i.@#)L > >>> > ) > >>> > > >>> > F (hcodes -:&:(#@>) deflatecodes) A > >>> > 1 > >>> > > >>> > There should be a better way of doing this, but this should at least > >>> > get you started. > >>> > > >>> > Thanks, > >>> > > >>> > -- > >>> > Raul > >>> > > >>> > > >>> > On Wed, Sep 10, 2014 at 10:45 AM, bill lam <[email protected]> wrote: > >>> > > For huffman coding used in zlib: > >>> > > https://www.ietf.org/rfc/rfc1951.txt section 3.2.2. > >>> > > > >>> > > The Huffman codes used for each alphabet in the "deflate" > >>> > > format have two additional rules: > >>> > > > >>> > > * All codes of a given bit length have lexicographically > >>> > > consecutive values, in the same order as the symbols > >>> > > they represent; > >>> > > > >>> > > * Shorter codes lexicographically precede longer codes. > >>> > > I tried jwiki hcodes in > >>> > > I try Roger's essay > >>> > > http://www.jsoftware.com/jwiki/Essays/Huffman%20Coding > >>> > > > >>> > > hc=: 4 : 0 > >>> > > if. 1=#x do. y > >>> > > else. ((i{x),+/j{x) hc (i{y),<j{y [ i=. (i.#x) -. j=. 2{./:x end. > >>> > > ) > >>> > > > >>> > > hcodes=: 4 : 0 > >>> > > assert. x -:&$ y NB. weights and words have same shape > >>> > > assert. (0<:x) *. 1=#$x NB. weights are non-negative > >>> > > assert. 1 >: L.y NB. words are boxed not more than once > >>> > > w=. ,&.> y NB. standardized words > >>> > > assert. w -: ~.w NB. words are unique > >>> > > t=. 0 {:: x hc w NB. minimal weight binary tree > >>> > > ((< S: 0 t) i. w) { <@(1&=)@; S: 1 {:: t > >>> > > ) > >>> > > > >>> > > but the coding produced is malformed for zlib. eg, > >>> > > this is what I ran into trouble > >>> > > > >>> > > f1=: 1 256 17 1 1 9 1 > >>> > > f2=: 2 1 0 1 255 0 1536 > >>> > > F=: ,/(f1#f2) > >>> > > A=: i.286 > >>> > > > >>> > > F hcodes A > >>> > > > >>> > > Or a shorter example > >>> > > > >>> > > A1=: i.12 > >>> > > F1=: 2 1 0 0 0 0 0 0 0 0 0 1 > >>> > > > >>> > > F1 hcodes A1 > >>> > > > >>> > > Any idea? > >>> > > > >>> > > -- > >>> > > regards, > >>> > > ==================================================== > >>> > > GPG key 1024D/4434BAB3 2008-08-24 > >>> > > gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3 > >>> > > gpg --keyserver subkeys.pgp.net --armor --export 4434BAB3 > >>> > > ---------------------------------------------------------------------- > >>> > > For information about J forums see http://www.jsoftware.com/forums.htm > >>> > ---------------------------------------------------------------------- > >>> > For information about J forums see http://www.jsoftware.com/forums.htm > >>> > > >>> ---------------------------------------------------------------------- > >>> For information about J forums see http://www.jsoftware.com/forums.htm > >>> > >> ---------------------------------------------------------------------- > >> For information about J forums see http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm -- regards, ==================================================== GPG key 1024D/4434BAB3 2008-08-24 gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3 gpg --keyserver subkeys.pgp.net --armor --export 4434BAB3 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
