Date   : Mon, 21 Jan 1985 20:41:27 GMT
From   : Bill Edwards <edwardsb@HARVARD.ARPA>
Subject: Re: Packed variables in Turbo Pascal

> 
> >    While messing around with Turbo Pascal last night I typed in the
> >    following short program:
> 
> >    |    program testvars;
> >    |
> >    |    var a : packed array [0..15] of boolean;
> >    |        b : set of 0..15;
> >    |
> >    |    begin
> >    |    writeln(sizeof(a),' ',sizeof(b));
> >    |    end.
> 
> >    The result was that variable 'a' took 16 bytes and 'b' took 2 bytes. A
> >    quick check of the manual revealed that the word 'packed' is ignored
> >    in Turbo; packing occurs automatically whenever possible. It certainly
> >    seems possible for packing to occur here. There is a compiler
> >    directive (*X- *) which supposedly causes the code size for arrays to
> >    be minimized, but the size is unchanged when I use this. It appears
> >    that Turbo is tuned for maximum speed, not minimum code size. Sets,
> >    however, use one bit per element, just as in UCSD Pascal.
> 
> >    Could someone try this on the 8088/8086 version of Turbo? I'm using
> >    the CP/M version on an Apple //e with a Z-80 card.
> 
> >    While we're on the subject, has anyone received info on new compilers
> >    from Borland? I keep hearing rumors of a Modula-2 compiler and an
> >    upgraded version of the Pascal compiler. Any news?
> 
> 
> >    Douglas Hall
> >    ITT Telecom Products
> >    Raleigh, NC
> >    ittvax!ittral!hall
> ----------------
> 
>    I have Turbo on an 8088.  It's the same story.  Turbo packs to the byte 
> level only; I'm told this is typical of Pascal implementations.  UCSD is 
> one of the few that packs to the bit level.  I did my test in a different 
> way: a case variant record where one variation was an array of boolean,
by which
> I wanted to access the bits of the other variation.  No good.  I had an 
> array of bytes where I wanted bits.
> 
>    Yes, Turbo's optimisation is definitely for speed; I believe they state as
> much.  I'm not sure, though, whether $X- is the right setting for optimised
> arrays.  Are sure that's not actually the default setting?
> 
>    As far as I'm aware Turbo's sets are bit vectors.  I think (hope, 
> certainly) that this is also typical of Pascal implementations (else why 
> impose such a ridiculous restriction as a 32-element set?).
> 
>    I too am eagerly awaiting reports of Borland's Modula-2.  Having separately
> compilable modules will make a great difference to me.  And with luck, the
> reams of additional features stuffed into Turbo will be separated into
> modules.  (Have you considered what the Turbo compiler's symbol must look
> like, not to mention the code to initialize it?!)
> 
>                   A. Milne

Rumor has it that they (despite Kahn's remarks about C being the
'American disease') are working on a C compiler.

                       Bill Edwards