Re: Streams in Ada

[Florian Weimer <fw@deneb.enyo.de>]

Robert A Duff <bobduff@world.std.com> writes:

> >...  There are quite a few Ada compilers out there which use
> > Storage_Element'Size = 8 even though it's inefficient on that
> > particular platform.
> 
> Which machines?  I've never heard of such a thing.

IIRC, in the AI dealing with 13.13.2(17), some vendor(s) claimed that
the current IA is inappropriate because it results in inefficient code
if a character is written to a stream because it has to be represented
in 8 bits.

With Storage_Element'Size, this isn't such a big concern, I think,
because usually, you can add all kinds of padding to make the
in-memory representation efficient.

> > An 8 bit char on a PDP-10 doesn't work.  Only values which are
> > divisors of 36 are acceptable.
> 
> I don't see why.  The PDP-10 hardware can deal with 8-bit bytes just
> fine (although you waste approx 1/9 of the bits).  Is there some
> subtlety of C I'm missing?

In C, each object must be representable as a sequence of bytes (i.e.
char values).  If you use 8-bit chars, words can only consist of 32
bits, not 36 bits.  So you have to run the PDP-10 in some kind of
32-bit mode.  As a result, you probably can't write system code in C.