Re: Ada and ASM

[Marin David Condic <nobody@noplace.com>]

True, it would be difficult to have some sort of "full-up" Ada syntax 
for assembler that was anywhere near portable across all machines. 
Unless you simply got to the point where you're compiling Ada anyway, so 
why bother? ;-)

However, I recall at least one Ada compiler that essentially defined 
something that looked like a discriminated record for assembler 
instructions and your assembler routines effectively looked like a set 
of agregates for the discriminated record where each aggregate 
represented the machine instruction you wanted. That was pretty much an 
"Ada Syntax" of sorts. Perhaps something along those lines with some 
semi-standard "macro-like" capabilities would be a good thing. (For 
example, if there were some flavor of "if" or "loop" statements that 
automagically expanded out into the corresponding machine instructions, 
that would be helpful and about all you'd need when you are dipping into 
assembler.)

MDC


Simon Wright wrote:
> 
> 
> All very well if all you wanted to do was move things about. But
> machines have all sorts of features, not all of which have
> counterparts on each architecture to be supported. What about reading
> the high-resolution clock? (rdtsc on Pentium, mftb on PowerPC).
> 
>    function Clock return Time is
>       type Half is (Low, High);
>       Lower, Upper : Interfaces.Unsigned_32;
>       Results : array (Half) of Interfaces.Unsigned_32;
>       Result : Time;
>       for Result'Address use Results (Low)'Address;
>    begin
>       System.Machine_Code.Asm
>         ("rdtsc" & ASCII.LF & ASCII.HT &
>            "movl %%eax, %0"& ASCII.LF & ASCII.HT &
>            "movl %%edx, %1",
>          Outputs => (Interfaces.Unsigned_32'Asm_Output ("=g", Lower),
>                      Interfaces.Unsigned_32'Asm_Output ("=g", Upper)),
>          Clobber => "eax, edx");
>       Results := (Low => Lower, High => Upper);
>       return Result;
>    end Clock;
> 
> is an Intel version, the PPC version (which I can't post) is quite
> different in structure. For a start, you have to read the timestamp in
> two bites! (on 32-bit implementations).
> 
> The major reason for using asm must be precisely to accommodate these
> sorts of differences.


-- 
======================================================================
Marin David Condic
I work for: http://www.belcan.com/
My project is: http://www.jast.mil/

Send Replies To: m c o n d i c @ a c m . o r g

     "In general the art of government consists in taking as
     much money as possible from one class of citizens to give
     to the other."

         --  Voltaire
======================================================================