Re: Ada And Alternate System Architectures

["Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org>]

Clearly, you need to read Chapter 13. If you are trying to do low level
system dependent things - or build things where the representation can be
controlled to be system independent, this is the chapter for you.

Specifically, see:

13.5.3 Bit Ordering
13.3 Representation Attributes

You can learn to use clever things like "for S'Bit_Order use
High_Order_First ;" and similar clever things by getting familiar with
Chapter 13.

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com
Web:      http://www.mcondic.com/


"Gary Scott" <Gary.L.Scott@lmtas.lmco.com> wrote in message
news:3B8549D8.A4E3A04A@lmtas.lmco.com...
> Hi,
>
> Thanks.  Fortran 95 defines a bit model for integers and then provides
> intrinsics for manipulating bits within that bit model.  What I was
> wanting was a key word optional argument for bit manipulation intrinsics
> that allowed me to very slightly modify the bit model by specifying an
> "endian" (byte) key word.  This would allow me to write "portable" code
> between big/little endian 8-bit byte systems.  Apparently if it's only
> 99.9% portable or acknowledges the existence of a "byte", it can't be
> considered.  I guess I understand, but it seems like this could be
> addressed through an architecture/system dependent modularized
> definition.
>
> Marin David Condic wrote:
> >
> > Ada bends over backwards to avoid specifying anything that would make it
> > impossible or impractical to implement Ada on just about any platform.
For
> > example, Ada specifies Streams which will most often be implemented as
8-bit
> > bytes, but the element type is defined in terms of some system defined
> > storage unit - so it could be 16-bit words or anything else you like.
> > Similarly, the standard integer types have a minimum range required. For
> > example, ARM 3.5.4(21) says:
> >
> > 21 In an implementation, the range of Integer shall include the
> > range -2**15+1 .. +2**15-1.
> >
> > That would suggest at least 16 bits - but it could be (and often is) 32
> > bits. On a PDP-10 it might be 36 bits.
> >
> > Ada does exist on processors that aren't 8-bit byte machines. The
> > Mil-Std-1750a comes immediately to mind.
> >
> > MDC
> > --
> > Marin David Condic
> > Senior Software Engineer
> > Pace Micro Technology Americas    www.pacemicro.com
> > Enabling the digital revolution
> > e-Mail:    marin.condic@pacemicro.com
> > Web:      http://www.mcondic.com/
> >
> > "Gary Scott" <Gary.L.Scott@lmtas.lmco.com> wrote in message
> > news:3B8528F1.7B664D21@lmtas.lmco.com...
> > > Hi,
> > >
> > > A very naive question...does the Ada standard adequately address
> > > non-8-bit byte computers?  The Fortran language standard committee
> > > consistently avoids defining anything that relates to a specific
> > > computer architecture implementation (because what if 6-bit character
> > > systems one day become common again...).  At a very high level, how
are
> > > machine specifics addressed?