At Tue, 24 Sep 2019 17:35:47 +0900 (Tokyo Standard Time), Kyotaro Horiguchi <horikyota....@gmail.com> wrote in <20190924.173547.226622711.horikyota....@gmail.com> > At Sun, 22 Sep 2019 23:02:04 -0300, Alvaro Herrera <alvhe...@2ndquadrant.com> > wrote in <20190923020204.GA2781@alvherre.pgsql> > > On 2019-Sep-22, Dmitry Dolgov wrote: > > > > > > I think multiplying two ScanDirections to watch for a negative result is > > > > pretty ugly: > > > > > > Probably, but the only alternative I see to check if directions are > > > opposite is > > > to check that directions come in pairs (back, forth), (forth, back). Is > > > there > > > an easier way? > > > > Maybe use the ^ operator? > > It's not a logical operator but a bitwise arithmetic operator, > which cannot be used if the operands is guaranteed to be 0 or 1 > (in integer). In a-kind-of-standard, but hacky way, "(!a != !b)" > works as desired since ! is a logical operator. > > Wouldn't we use (a && !b) || (!a && b)? Compiler will optimize it > some good way.
Sorry, it's not a boolean. A tristate value. From the definition (Back, NoMove, Forward) = (-1, 0, 1), (dir1 == -dir2) if NoMovement did not exist. If it is not guranteed, (dir1 != 0 && dir1 == -dir2) ? regards. -- Kyotaro Horiguchi NTT Open Source Software Center
