On Thu, Feb 27, 2020 at 9:46 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
>
> On Tue, Feb 25, 2020 at 11:49 PM Nicolas Iooss <nicolas.iooss@xxxxxxx> wrote:
> > As ebitmap_get_bit() complexity is linear in the size of the bitmap, the
> > complexity of ebitmap_cardinality() is quadratic. This can be optimized
> > by browsing the nodes of the bitmap directly in ebitmap_cardinality().
> >
> > While at it, use built-in function __builtin_popcountll() to count the
> > ones in the 64-bit value n->map for each bitmap node. This seems better
> > suited than "count++". This seems to work on gcc and clang on x86,
> > x86_64, ARM and ARM64 but if it causes compatibility issues with some
> > compilers or architectures (or with older versions of gcc or clang),
> > the use of __builtin_popcountll() can be replaced by a C implementation
> > of a popcount algorithm.
> >
> > Signed-off-by: Nicolas Iooss <nicolas.iooss@xxxxxxx>
> > ---
> > libsepol/src/ebitmap.c | 9 +++++----
> > 1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/libsepol/src/ebitmap.c b/libsepol/src/ebitmap.c
> > index d23444ce5064..a5108b7184c5 100644
> > --- a/libsepol/src/ebitmap.c
> > +++ b/libsepol/src/ebitmap.c
> > @@ -128,14 +128,15 @@ int ebitmap_andnot(ebitmap_t *dst, ebitmap_t *e1, ebitmap_t *e2, unsigned int ma
> >
> > unsigned int ebitmap_cardinality(ebitmap_t *e1)
> > {
> > - unsigned int i, count = 0;
> > + unsigned int count = 0;
> > + ebitmap_node_t *n;
> >
> > if (e1->cardinality || e1->highbit == 0)
> > return e1->cardinality;
> >
> > - for (i=ebitmap_startbit(e1); i < ebitmap_length(e1); i++)
> > - if (ebitmap_get_bit(e1, i))
> > - count++;
> > + for (n = e1->node; n; n = n->next) {
> > + count += __builtin_popcountll(n->map);
> > + }
> > e1->cardinality = count;
> > return count;
> > }
> > --
> > 2.25.0
> >
>
> Acked-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
>
> I'll check if the cardinality caching still makes any measurable
> difference and if not, I'll post a revert patch.
Thanks. I applied this patch.
Nicolas
