http://www.freepascal.org/docs-html/rtl/system/move.html

I have a working function in assembler wich copys a memory block from sorce to destination.

Now I want it to do with the move function from unit system, but it does not work.

procedure wd_copy( s , d : pointer ; l : longint );
begin
 move( s , d , l ); // does not work! Access violation errors
end;

procedure wd_copy( s , d : pointer ; l : longint ); begin
if l > 0 then begin

  if d < s then begin
   asm
     pushf
     mov   esi,s
     mov   edi,d
     mov   ecx,l
     cld              // vorwärts
     rep   movsb
     popf
   end['EAX','EBX','ECX','EDX','ESI','EDI'];
  end
  else begin
   asm
     pushf
     mov   esi,s
     add   esi,l
     dec   esi
     mov   edi,d
     add   edi,l
     dec   edi
     mov   ecx,l
     std              // rückwärts
     rep   movsb
     popf
   end['EAX','EBX','ECX','EDX','ESI','EDI'];
  end;

end;
end;

.
.

Move (S^, D^, L)

should do it.

Tomas

Yes, thanks.

I am confused with the meaning of

const source;

and

var dest;

Is there a description of the behaviour of const and var in this case? Why is it not both const or both var?

2013/11/13 Rainer Stratmann

"source" is where the data "comes from", so the procedure won't modify it (if there is no memory overlap between source and dest), so it is declared as "const"
"dest" is where the data is copied to, so the procedure will necessarily modify it (if "count" is 0), and the procedure should modify so it is declared as "var". Actually, IMO it could be declared as "out", this would avoid a meaningless warning.

But why does it work without specifying the vars more exactly like in other cases?

2013/11/13 Rainer Stratmann

You mean, how can it work without using typed variables? In Pascal, you don't have to give the type of a parameter, although 99.99% of the times you should do it. If you don't do it, you could as well use assembly :-) Actually, that's probably how Move is written: in assembly language. Of course, since the types were not given in the parameter declaration of Move, the compiler can't know the size of the data, and you have to give the compiler some indication. That's what "count" is for. Move considers the memory as 2 big arrays of bytes, one starting at "source", and the second at "dest".

The fallback implementation (for new architectures) is written in Pascal. See $fpcdir\rtl\inc\generic.inc.

Regards,
Sven

2013/11/13 Sven Barth

Of course it is, I should have guessed it, Lazarus/FPC is multi-platform. I keep thinking as if I was using a Windows-only development tool.

Most architectures do have a (often much shorter) implementation in assembly language though which is located in $fpcdir\rtl\$cpu\$cpu.inc.

Regards,
Sven

Is there a description of the behaviour of const and var in this case?

Not so clear: http://www.freepascal.org/docs-html/ref/refsu59.html A liiiitle bit clearer:
http://docwiki.embarcadero.com/RADStudio/XE5/en/Parameters_(Delphi)#Untyped_Parameters

Why is it not both const or both var?

If the Dest is const, then it cannot be written to. If Src is var, then the value might be modified while it's not expected to be. Moreover, const has no exact passing mechanism, the compiler may choose to pass by reference or value. Var is always by reference, another reason to mark Dest as var.