[fpc-pascal]runtime 201 with swapword function

[Jonas Maebe]

On vrijdag, jul 25, 2003, at 16:22 Europe/Brussels, James Mills wrote:

> Why does the following result in a runtime error ?
>
> program example;
>
> const
> 	THE_PORT = 9999;
>
> function swapWord(w: Word): Word;
> begin
> 	swapWord := (w SHL 8) OR (w SHR 8);
> end;

In Pascal, all calculations are performed using the base type (which is 
longint in FPC), so if w > 255, then w shl 8 > high(word) and will 
result in a range check error when assigning to swapWord. Even if we 
calculated everything using words, you'd still get an overflow error, 
this time when doing the shl.


Jonas