On Fri, Jul 25, 2003 at 04:21:36PM +0200, Jonas Maebe wrote:
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.
How can I correct this ? This bit of code was taken directly from server.pp in one of the old 2002 mailing threads...
Turn range checking off for this piece of code or do
function swapWord(w: Word): Word;
begin
swapWord := ((w SHL 8) OR (w SHR 8)) and $ffff;
end;
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