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From: akcs.joehorn@hpcvbbs.UUCP (Joseph K. Horn)
Newsgroups: comp.sys.handhelds
Subject: HP 48 Faster PGDIR
Message-ID: <284dca48:3374comp.sys.handhelds@hpcvbbs.UUCP>
Date: 6 Jun 91 05:40:08 GMT
Lines: 85

FPGDIR, a FAST PGDIR, by Joseph K Horn.  Makes PGDIR obsolete.

When you use PGDIR on a very large directory, it can take a long time
to finish.  For example, I just used Donnelly's XTIME function to time
PGDIR on a big directory, and it took a painful 50 seconds!

Bill Wickes explains why in his excellent book, "HP 48 Insights":

     "PGDIR removes a directory specified by name.  It does
      this by recursively executing CLVAR and PURGE recursively
      on each subdirectory until the original directory is
      empty.  (This process can take a relatively long time if
      the directory is large.)"  [Part I, page 96]

Guess what!  There's a better way!

Those of you with HP-41CX's will remember the CLRALMS command that
cleared all the alarms out.  If you had a lot of alarms, it took a
long time to finish, because it looped through the alarm buffer
clearing each one individually.  But a much better way was to treat
the entire buffer as one object, and clear it in one fell swoop.
This was possible with the buffer clearing functions available in
several plug-in ROMs.  For example, with the Extended-IL ROM, just
execute 10 CLRBUF, and instantly the entire alarm buffer gets
cleared, no matter how large it is.

It turns out that there is a similar trick for purging directories
on the HP 48.  Rather than painfully looping through them, clearing
their contents, we can treat the whole thing as a single object and
PURGE it in one fell swoop.

Here's the trick.  The HP 48 Owner's Manual says:

     "Once a directory is empty, you can purge it like any
      other variable -- put its name on the stack and execute
      PURGE."  [Volume 1, page 123]

But "empty" means "when VARS == { }".  And VARS == { } when all
the vars are "hidden" behind a null-named object (see NULLNAME.DOC
on Goodies Disk #1).

So the quick way to purge a directory is:

(1) Put its name on the stack;
(2) Get into that directory: DUP EVAL;
(3) Unhide everything (just in case): '' PURGE;
(4) Hide all its vars: 0 '' STO;
(5) Go back to the parent directory: UPDIR;
(6) Purge the "empty" directory: PURGE.

This process is automated by the following replacement for PGDIR:

---------------------< FPGDIR >---------------------------------
%%HP:T(1);
\<<
    IF DUP TYPE 6 ==
    THEN
      IF DUP VTYPE -1 ==
      THEN DROP
      ELSE
        IF DUP VTYPE 15 ==
        THEN DUP EVAL 0 # 15777h SYSEVAL DUP PURGE STO UPDIR PURGE
        ELSE 515 DOERR
        END
      END
    ELSE 514 DOERR
    END
\>>
----------------------------------------------------------------

Except for its improved speed, its action is exactly like PGDIR.
It even generates the same error messages as PGDIR in case of bad
arguments.  Nonexistent names simply get dropped (like PGDIR does).

To use: place name of directory on stack, and run it.

It does full argument type checking, so it should be idiot proof.

I keep it assigned to my blue-shifted DEL key.  That way it takes only
three keystrokes to delete a directory (tic, menu, FPGDIR).

It should be in "system RPL" ... but that's left as an exercise for
the reader.  :-)

--  Joseph K Horn  --  Peripheral Vision, Ltd.  --