[fpc-pascal] Move with pointers to memory

Sven Barth pascaldragon at googlemail.com
Wed Nov 13 11:19:36 CET 2013

Am 13.11.2013 11:07, schrieb Frederic Da Vitoria:
> 2013/11/13 Rainer Stratmann <rainerstratmann at t-online.de 
> <mailto:rainerstratmann at t-online.de>>
>      On Wednesday 13 November 2013 10:52:23 you wrote:
>     > 2013/11/13 Rainer Stratmann <rainerstratmann at t-online.de
>     <mailto:rainerstratmann at 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.

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