Re: Ada And Alternate System Architectures

[Gary Scott <Gary.L.Scott@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?