RISC

["chris.danx" <chris.danx@ntlworld.com>]

Hi,
    I'm simulating a RISC machine in Ada.  Eventually the instructions will
be mapped to native architecture (x86, m68xxx, SPARC, etc), but for now i
want to simulate a machine, to limit the possibility of doing something
nasty to anyone's machine.

I've decided to provide byte, word and long word  modes for most
instructions.  The problem comes when clearing or setting byte or word
portions of a register (the machine is loosely based on M68000).  The
register is long word (32bit) and i want to set the lower 16bits or 8bits.
I've managed to get this to work, problem is it's not very efficient.

The register is of type 'mod', so i divided by 2**8 or 2**16 then multiplied
by it.  I know multiplication and division are costly and really i'm looking
for something more efficient.  If this were Pascal i'd use 'shift
left/right' which is quite fast.  What should i do to speed it up?  Does Ada
have a shift L/R operation?  Is there another way to do it?

I have another problem with memory.  I thought about allocating one big
block of memory (as an array) and accessing it by index.  The problem?  I do
plan to dynamically allocate the memory, but i'll still be limited by the
amount of memory allocable in a single array.  I've thought of a few ways of
doing this but can't seem to avoid problems!  Anyone know of a solution?  I
don't like using C, but i 'd run in to a similar problem binding with C
anyway.


Thanks,
Chris Campbell

p.s. This isn't a homework assignment!!!