assume av=1001, am = 1000, bv=1000, bm=1001.
Should dv's last bit be zero? if not, then my interpretation of what
this function does
is wrong.
On Mon, Apr 6, 2015 at 9:31 PM, Ben Pfaff <b...@nicira.com> wrote:
> On Mon, Apr 06, 2015 at 03:28:37PM -0700, Andy Zhou wrote:
>> On Tue, Mar 31, 2015 at 9:52 PM, Ben Pfaff <b...@nicira.com> wrote:
>> > To be first used in upcoming commits.
>> >
>> > Signed-off-by: Ben Pfaff <b...@nicira.com>
>>
>> > +/* Consider the two value/mask pairs 'a_value/a_mask' and
>> > 'b_value/b_mask' as
>> > + * restrictions on a field's value. Then, this function initializes
>> > + * 'dst_value/dst_mask' such that it combines the restrictions of both
>> > pairs.
>> > + * This is not always possible, i.e. if one pair insists on a value of 0
>> > in
>> > + * some bit and the other pair insists on a value of 1 in that bit. This
>> > + * function returns false in a case where the combined restriction is
>> > + * impossible (in which case 'dst_value/dst_mask' is not fully
>> > initialized),
>> > + * true otherwise. */
>> > +bool
>> > +mf_subvalue_intersect(const union mf_subvalue *a_value,
>> > + const union mf_subvalue *a_mask,
>> > + const union mf_subvalue *b_value,
>> > + const union mf_subvalue *b_mask,
>> > + union mf_subvalue *dst_value,
>> > + union mf_subvalue *dst_mask)
>> > +{
>> > + for (int i = 0; i < ARRAY_SIZE(a_value->be64); i++) {
>> > + ovs_be64 av = a_value->be64[i];
>> > + ovs_be64 am = a_mask->be64[i];
>> > + ovs_be64 bv = b_value->be64[i];
>> > + ovs_be64 bm = b_mask->be64[i];
>> > + ovs_be64 *dv = &dst_value->be64[i];
>> > + ovs_be64 *dm = &dst_mask->be64[i];
>> > +
>> > + if ((av ^ bv) & (am & bm)) {
>> > + return false;
>> > + }
>> > + *dv = av | bv;
>> > + *dm = am | bm;
>> Should this be *dv = (av & am) | (bv & bm)? I have not read the following
>> patch
>> to check the actual usage, so my interpretation of 'intersect' may be
>> different than
>> what's intended here.
>
> I think that in the cases where the expression you suggest would have a
> different value, the "if" statement just before would have bailed out.
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