Re: xor as a lazy comparison

Grant Coady
2005-07-24T20:08:04Z

On Sun, 24 Jul 2005 18:40:25 +0200 (MEST), Jan Engelhardt <jengelh@linux01.gwdg.de> wrote:
>
>I have seen this in kernel/signal.c:check_kill_permission()
>
> && (current->euid ^ t->suid) && (current->euid ^ t->uid)
>
>If current->euid and t->suid are the same, the xor returns 0, so these
>statements are effectively the same as a !=
>
> current->euid != t->suid ...
>
>Why ^ ?
To confuse you, coders with assembly or hardware background throw in
equivalent bit operations to succinctly describe their visualisation
of solution space... Perhaps the writer _wanted_ you to pause and
think? Maybe the compiler produces better code? Try it and see.

Grant.