Date: Sat, 23 Mar 1991 21:10 CST
Subject: HP-48 Library Objects
Lines: 39


   I have two additions to make to James Cloos' and Dave Kaffine's
postings (November 15, and November 16, 1990, respectively) on the
composition of library objects.

   For clarification, a command number is the second of the two XLIB
numbers, and is used to index the command within its library. The
library is indexed by the library number, which is the first of the
two numbers, and is used to locate the library.

   First, when allocating command numbers, the named commands must use
the low end of the range, and the unnamed commands the upper. For
instance, if the library is to contain two names commands "ONE" and
"TWO", and in addition to that two unnamed commands, then the named
commands must be commands number 0 and 1, and the unnamed commands 2
and 3.

   Second, the back pointers in the hash table are ordered by command
number (for the named commands - the hash table is used for name
translations), and of course only the named commands are included.
The order of the back pointers (and, thus, the command numbers) decide
in what order the commands appear in the LIBRARY menu.

   As I mentioned, the commands are ordered in the menu according to
the back pointers. But they are executed by indexing the link table,
so the two better match - or the keys will not match the functions,
and if you, like I did, name commands for debugging purposes, then
running the wrong code object may have disastrous results!

   Finally, I have a question which someone may be able to answer:
when storing a library in a port, or attaching it, does it run a risk
of getting split up and the different parts of it moved around
independently, or will it be stored as one continuous chunk of memory?
More specifically, can CODE objects in the library share subroutines
and (potentially large) tables? I'm sure they're not going to get
split up if in ROM ;-), but what about when they're in RAM?

						-- Jan Brittenson
						   bson@ai.mit.edu