Re: RISC

[Robert A Duff <bobduff@world.std.com>]

"Marin David Condic" <marin.condic.auntie.spam@pacemicro.com> writes:

> Yea Verily And For Sooth! So long as we are going to have to deal with
> hardware designed by hardware engineers (instead of compiler writers) or
> communicate with data streams that come from places not programmed in Ada,
> *someone* is going to create data that needs really bizarre representations.

Bill Wulf wrote something along the lines of:  People who design overly
complicated hardware should be punished by being forced to write
compilers that target to that hardware.

> From a practical perspective, I don't think it is that much of an issue. In
> theory, someone might one day (again) make a machine that deals with sixbit
> data.

I'll bet that doesn't happen in my lifetime.  ;-)

>... What is the likelihood there will be a huge demand for Ada compilers
> for such a machine? Most machines these days are byte oriented. You've got
> to deal with byte sex, but beyond that you can pretty much count on hardware
> having some sort of support for byte sized data. It shouldn't be that tough
> to map most rep clauses onto that sort of machine.

Even if all machines had 8-bit bytes and 32-bit words, you still want
different code depending on whether a bit-field crosses a word boundary.
Different code = complexity.

As you say, endianness is still a problem.

And I'm currently supporting an Ada compiler for a machine whose
Storage_Unit = 32, rather than the more common 8.

By the way, nesting of records within records and arrays also introduces
complexity (again, if you require efficiency).

I once worked on an Ada prototype compiler (around 1982), which ignored
efficiency, and did everything in one general way that always worked.
The generated code was intolerable.  For example, to do "X := Y;" where
X and Y are of type Integer, it copied each of the 36 bits individually
(it was a PDP-10, which is a 36-bit word-addressable machine).
Totally useless.

- Bob