You wind up using a loop or something equivalent to a loop. A lot of rfcs specify looping algorithms. So... using loops when implementing support for those algorithms seems like the right choice.
That said, /\. can be used to construct loop-like behavior, if you must. Thanks, -- Raul On Mon, Sep 1, 2014 at 1:44 AM, bill lam <[email protected]> wrote: > Context for discussion, section 6.6 of this png rfc > > * http://tools.ietf.org/html/rfc2083 > > The forward filter seems trivial, but the backward filter seems > tricky to me if not using loop. Any idea on a loop free > solution? > > > NB. Paeth Predictor > paeth=: 3 : 0 > p=. +/ 1 1 _1 * y > y{~ (i.<./) |p-y > ) > > forward=: 4 : 0 > prev=. 10$ 3 5 8 > iy=. i.10 > pae=. 256&| iy - paeth"1 ((-x)}.(x#0),iy),.prev,.((-x)}.(x#0),prev) > ) > > 3 forward'' > 253 252 250 3 3 3 3 3 3 3 > 4 forward'' > 253 252 250 0 1 0 4 2 0 6 > > NB. backward ?? > NB. 4 backward 4 forward '' > > -- > 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
