Bit Switching - How?

[David Goodenough]

>From article <10007 at smoke.BRL.MIL>, by gwyn at smoke.BRL.MIL (Doug Gwyn ):
> In article <626 at gonzo.UUCP> daveb at gonzo.UUCP (Dave Brower) writes:
>>>		x ^= z, y^= z;		/* flip those that do */
> -		x ^= z; 		/* flip those that do */
> -		y^= z;
> -If you don't see _why_ this is the right way, you'd better not work on a
> -project with anyone but yourself.
> 
> Hey, now, it's not all that clear cut.  Conceptually the two
> assignments should occur in parallel; for some people using , to
> separate such assignments is the "natural" way to express that.

In either case, the assignments happen one after the other. As far as
I know, C has no equivalent to the BCPL mechanism:

		a,b := b,a

Which is what we were trying to do in the first place :-) I would add
that the comma operator has it's place, and there is nothing wrong with
saying:

#define		swap(a, b)	((a) ^= (b), (b) ^= (a), (a) ^= (b))

except the ususal caveats about lvalues and side effects. Think what

	swap(i, getchar())

Would do :-) [Ouch]
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