September 95 - Newton Q & A: Ask the Llama
Q I have a program that communicates with the desktop. Part of the information
sent is real numbers. I've found functions to stuff almost every other type of
data into a binary object except real numbers. How do I do that?
A You have two choices. First, you could just print the real number as a string
(using SPrintObject), send the string, and convert it back on the other side.
Clearly this isn't a good idea if you want to maintain a high degree of
precision. The other choice is to construct the correct type of binary object
for the target desktop machine. In other words, take the Newton real
representation and convert it into, say, IEEE floating point. Then you can use
BinaryMunger to stuff the binary object into whatever packet of data you're
constructing.
Note that Newton uses SANE representation for real numbers that are in the
representable range. However, the representation of exceptions (such as NAN and
infinity) are different and undocumented. At this time you should avoid
converting these types of real numbers.
Q Can you give me a short and clear description of the different types of
Newton memory?
A There are three important "pools" of so-called internal memory, each with
different tradeoffs.
The NewtonScript heap (about 90K to 96K on current devices) is where all the
runtime data from NewtonScript lives. Any result from the Clone family of calls
will take up NewtonScript heap space. The view frame made at run time from your
application templates will take up this heap space. NewtonScript heap space is
very precious, so you should try to use as little of it as possible, especially
when your application's base view isn't open.
The user store (192K in the MessagePad 100, larger on other devices) is where
application packages stored internally live, and where soups are located. The
entries in the soups are located in this space. While not quite as precious as
the NewtonScript heap, this space can certainly run out. This is the space
that's "extended" when a RAM PCMCIA card is inserted.
There is also some system heap space, which is used for, well, everything else.
The viewCObjects and drawing objects live here. Recognition uses memory from
here. You can run out of this space (in which case you get the Cancel/Restart
dialog) but it's less of a programming issue.
Q I have an application that uses a protoRollBrowser. When I expand the items,
they have lines separating them. I can't seem to get rid of them. Is this a
bug?
A What you're seeing is part of the default definition of a protoRollItem. It
includes a 1-pixel border. You can remove that border by modifying the
viewFormat of your rollItems. In addition, you may want to set the fill to
white.
Q I'm using a protoRoll (not protoRollBrowser) in my application. But it never
shows up. What's the problem?
A You need to give it a viewFlags slot and make sure the Visible bit is
checked. The default is Application and Clipping, but this won't make the
protoRoll visible if it's included inside another view.
Q I have a text view that the user can use to enter text. I wanted to extend a
selection. I knew the insertion caret was at the end of the selection, so I
called SetHilite(newPoint, newPoint, nil), where newPoint is the new position
for the selection extension, but I got no highlight. What's going wrong?
A The behavior is actually perfectly correct. There's a not quite obvious
interaction between the caret and SetHilite. As shown in the table below, how
SetHilite behaves depends on four things: the start and end character positions
(the first two arguments) being equal, the value of unique (the third
argument), the presence of a previously highlighted selection, and the presence
of the caret. Note that the following explanation refers to the case of a
single paragraph view, in which there can be only one selection; if there are
multiple paragraph views, it's possible (with unique nil) to have multiple
discontiguous selections.
Q I have an application that uses ADSP to connect to a server on the desktop. I
want the server to handle multiple Newtons connected simultaneously.
Unfortunately, if a connection fails after it's opened, the server doesn't seem
to be able to identify it as a new connection when the Newton reconnects. This
causes problems in the server's ability to handle multiple connections. Can you
help?
A We'll assume that the Newton tries to reconnect shortly after losing the
connection. In that case, the Newton doesn't generate a new connection ID, so
your server probably acts as if the connection didn't close, while the Newton
is acting as if it's establishing a new connection. Currently the only solution
is to force the Newton to wait three minutes after an improper disconnect
before trying to reconnect.
Q I have a communications program that always sends a string of the same size
to the desktop. The string is quite large, and I would like to preallocate it
and fill it with a particular value. What's the best way to do this?
A As with all things in programming, the answer is a tradeoff between space and
time. Let's assume that you want a string of 2K characters filled with the
character A, and that you control the contents of the string (that is, if you
get user input, you make sure the input is a string). The first option is to
allocate the string at compile time. Note that you shouldn't allocate your
string constant with a double-quoted string ("a string"), since typing 2K (less
the terminator) characters is monotonous and error prone. The way to allocate
the string is with the following SetLength trick:
constant kNumberOfUnicodeCharsForString := 2048; // 2K chars
DefConst('kMyBigString, call func()
begin
// SetLength uses bytes; Unicode chars are 2 bytes each
local aStr := SetLength("",
2 * kNumberOfUnicodeCharsForString + 2);
// initialize the string
for i := 0 to k1KUnicodeChars - 1 do
aStr[i] := $A;
return aStr;
end with ());
At
run time you can clone kMyBigString and do what you need to fill it with
characters. Note that the object is not a string; you would need to use
StuffByte to put in individual characters.
The advantage of this method is that it's very fast: it averages less than one
tick (60th of a second) for the clone. The disadvantage is that it puts a 4K
object in your package (Unicode strings are two bytes per character). If you
can't afford the 4K in your package, you need to generate the string at run
time. Using the above code at run time averages 52 ticks.
Another possible runtime method is to use smart strings, which allow you to
preallocate strings and concatenate them in a more efficient way. The first
attempt at doing this seems to be inefficient, at an average of 175 ticks:
// defined constant somewhere in your project
constant kNumberOfUnicodeCharsForString := 2048;
local s := SmartStart(2 * kNumberOfUnicodeCharsForString + 2);
local l := 0;
for i := 1 to kNumberOfUnicodeCharsForString do
l := SmartConcat(s, l, "A");
SmartStop(s, l);
However,
simply concatenating two characters at a time reduces the average to 88 ticks;
four characters reduces it to 44; and so on. A lesson here is that testing and
measurement are your friends.
Q I'd like to train my dog to code in NewtonScript. How can I do that?
A I'm afraid the prospect isn't promising. Dr. J. L. Fredericks at SITAP
(Stanford Institute for Training Animal Programmers) has been trying for ten
years to train different animal species to program computers. Although he's had
some success training dogs to do simple programs, he says, "Anything more than
a simple statement is beyond them. No loops, no conditionals." Besides which,
paws don't work well for moving mice. For Newton programming the best he has
been able to achieve is training a rat to reset the Newton on command. As Dr.
Fredericks says, "Never underestimate the usefulness of a ratset."
The llama is the unofficial mascot of Developer Technical Support in Apple's
Newton Systems Group. Send your Newton-related questions to NewtonMail DRLLAMA
or AppleLink DR.LLAMA. The first time we use a question from you, we'll send
you a T-shirt.*
Thanks to our Newton Partners for the questions used in this column, and to
jXopher Bell, Bob Ebert, David Fedor, Neil Rhodes, Jim Schram, Maurice Sharp,
and Bruce Thompson for the answers. Thanks especially to Bob Ebert for the
Newton memory description.*
Have more questions? Take a look at Newton Developer Info on AppleLink.*
