Re: xor as a lazy comparison
From: Steven Rostedt
Date: Mon Jul 25 2005 - 14:27:32 EST
On Mon, 2005-07-25 at 12:16 -0700, Philippe Troin wrote:
> Lee Revell <rlrevell@xxxxxxxxxxx> writes:
> > On Mon, 2005-07-25 at 13:55 -0400, Steven Rostedt wrote:
> > > Doesn't matter. The cycles saved for old compilers is not rational to
> > > have obfuscated code.
> > Where do we draw the line with this? Is x *= 2 preferable to x <<= 2 as
> > well?
> Depends if you want to multiply by 2 or 4 :-)
I guess this proves my point :-)
But lets look at the signal.c code as well:
if ((!info || ((unsigned long)info != 1 &&
(unsigned long)info != 2 && SI_FROMUSER(info)))
&& ((sig != SIGCONT) ||
(current->signal->session != t->signal->session))
&& (current->euid ^ t->suid) && (current->euid ^ t->uid)
&& (current->uid ^ t->suid) && (current->uid ^ t->uid)
Why did they do the (current->signal->session != t->signal->session) and
not also do (current->signal->session ^ t->signal->session)?
Bit shifting for doubling (or quadrupling) may or may not be confusing,
(I don't mind that), but using xor for non-equal is IMO past that line.
Since, I usually use xor for bit masks. Looking at the above code,
especially since it is not always used, I would think that euid, uid,
and suid are all bitmasks.
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