Re: 80286 protected mode

On 2024-10-12 21:33, Brett wrote:

David Brown <david.brown@hesbynett.no> wrote:

On 12/10/2024 01:32, MitchAlsup1 wrote:

On Fri, 11 Oct 2024 22:02:32 +0000, David Brown wrote:
>

On 11/10/2024 20:55, MitchAlsup1 wrote:

On Fri, 11 Oct 2024 12:10:13 +0000, David Brown wrote:
>

>
Do you think you can just write this :
>
void * memmove(void * s1, const void  * s2, size_t n)
{
     return memmove(s1, s2, n);
}
>
in your library's source?

>
        .global memmove
memmove:
        MM     R2,R1,R3
        RET
>
sure !

>
You are either totally clueless, or you are trolling.  And I know you
are not clueless.
>
This discussion has become pointless.

>
The point is that there are a few things that may be hard to do
with {decode, pipeline, calculations, specifications...}; but
because they are so universally needed; these, too, should
"get into ISA".
>
One good reason to put them in ISA is to preserve the programmers
efforts over decades, so they don't have to re-write libc every-
time a new set of instructions come out.
>
Moving an arbitrary amount of memory from point a to point b
happens to fall into that universal need. Setting an arbitrary
amount of memory to a value also falls into that universal
need.

>
Again, I have to ask - do you bother to read the posts you reply to?
Are you interested in replying, and engaging in the discussion?  Or are
you just looking for a chance to promote your own architecture, no
matter how tenuous the connection might be to other posts?
>
Again, let me say that I agree with what you are saying - I agree that
an ISA should have instructions that are efficient for what people
actually want to do.  I agree that it is a good thing to have
instructions that let performance scale with advances in hardware
ideally without needing changes in compiled binaries, and at least
without needing changes in source code.
>
I believe there is an interesting discussion to be had here, and I would
enjoy hearing about comparisons of different ways things functions like
memcpy() and memset() can be implemented in different architectures and
optimised for different sizes, or how scalable vector instructions can
work in comparison to fixed-size SIMD instructions.
>
But at the moment, this potential is lost because you are posting total
shite about implementing memmove() in standard C.  It is disappointing
that someone with your extensive knowledge and experience cannot see
this.  I am finding it all very frustrating.

 

   [ snip discussion of HW ]

In short your complaints are wrong headed in not understanding what
hardware memcpy can do.

I think your reply proves David's complaint: you did not read, or did not understand, what David is frustrated about. The true fact that David is defending is that memmove() cannot be implemented "efficiently" in /standard/ C source code, on /any/ HW, because it would require comparing /C pointers/ that point to potentially different /C objects/, which is not defined behavior in standard C, whether compiled to machine code, or executed by an interpreter of C code, or executed by a human programmer performing what was called "desk testing" in the 1960s.
Obviously memmove() can be implemented efficently in non-standard C where such pointers can be compared, or by sequences of ordinary ALU instructions, or by dedicated instructions such as Mitch's MM, and David is not disputing that. But Mitch seems not to understand or not to see the issue about standard C vs memmove().