[DUG] for..loop

[Neven MacEwan]

John

This is where 'optimisation' comes in it  would count down  because  
'jump zero' is a single instruction but
would only apply this if there was no reference to the loop var ie

var
  i: integer

for i:= 0 to 3 do
begin
  write('hello')
end;

but don't do
for i:= 0 to 3 do
begin
end;

because many optimisers will remove this loop altogether

Neven

> That sort of surprises me - surely counting down instead of up would spoil
> the expected logic of a loop in some cases????
>
> Eg a trivial example, getting the first word from a string...
>
> Function getfirstword(aline:string):integer;
> Var
> i:integer;
> For i:=1 to length(aline) do
> Begin
>    if(aline[i]=' ') then
>    begin
>      result:=copy(aline,1,i-1);
>      exit;
>    end;
> End;
>
> I would indeed be rather upset if I got either the last word back, or the
> whole of the line except the last word.
> This is a made up example, but I am sure a lot of "for" loops might be
> looking for the first instance of something...are you saying we cannot rely
> on the order the loop runs???
>
> John
>
>   
>> p.s. has anyone else noticed that sometimes when you step through a 
>> for loop the counter actually counts down (in the debugger) (even if 
>> it set to count up).  This was the case sometimes in D6 if I recall 
>> correctly.
>>
>>     
>
> It's an optimisation thing.  Counting down to 0 is more efficient than
> counting up.
>
> Sean
>
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