Re: Possible type with bitwise operator (&)

3 Aug 2020


      On 03/08/2020 15.44, Gregory Burd wrote:
...
Sjoerd,
Nice explanation, so if they are both correct and one avoids unnecessary
work (even just a tiny bit) why not adjust the code to add your
explanation as a comment and use the more efficient version?
In the one case you have an extra evaluation (of a bit), in the other
case you have possibly a jump.  If the jump cannot be predicted by the
CPU, it is definitely more expensive than the extra evaluation.
...
-greg
On Mon, Aug 3, 2020 at 3:02 AM Sjoerd Mullender mailto:sjoerd@monetdb.org> wrote:
Either way is correct.
    The first form evaluates both (b->ttype != TYPE_void) and b->tkey, both
    of which result in either 0 or 1.  The single & does a bit-wise AND on
    those two values and results in 1 if both sides evaluated to 1.
    In the second form, if first part evaluates to 0, b->tkey is not
    evaluated, and if the first part evaluates to 1, the second part is also
    evaluated.  The restult, again, is only 1 if both sides evaluate to 1.
So the difference is whether or not b->tkey is evaluated, and evaluating
    that is cheap (it's a bool value).
On 01/08/2020 20.54, Ranier Vilela wrote:
    > Hi,
    >
    > At gdk\gdk_bat.c (line 1384)
    > variable b->type is bool
    >
    > Would be a typo?
    > if (((b->ttype != TYPE_void) & b->tkey) && b->batCount > 1) {
    > Should be:
    > if (((b->ttype != TYPE_void) && b->tkey) && b->batCount > 1) {
    >
    > regards,
    > Ranier Vilela
    >
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