Am 13.11.2013 11:32, schrieb Frederic Da Vitoria:
2013/11/13 Sven Barth <pascaldra...@googlemail.com
<mailto:pascaldra...@googlemail.com>>
Am 13.11.2013 11:07, schrieb Frederic Da Vitoria:
2013/11/13 Rainer Stratmann <rainerstratm...@t-online.de
<mailto:rainerstratm...@t-online.de>>
On Wednesday 13 November 2013 10:52:23 you wrote:
> 2013/11/13 Rainer Stratmann <rainerstratm...@t-online.de
<mailto:rainerstratm...@t-online.de>>
> > Is there a description of the behaviour of const and var
in this case?
> > Why is it not both const or both var?
>
> "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?
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.
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
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