On 16 June 2016 at 18:12, Dr. David Alan Gilbert (git) <dgilb...@redhat.com> wrote: > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > e.g. BIT_RANGE(15, 0) gives 0xff00 > > Suggested by: Paolo Bonzini <pbonz...@redhat.com> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > --- > include/qemu/bitops.h | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h > index 755fdd1..e411688 100644 > --- a/include/qemu/bitops.h > +++ b/include/qemu/bitops.h > @@ -23,6 +23,9 @@ > #define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG)) > #define BIT_WORD(nr) ((nr) / BITS_PER_LONG) > #define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * > sizeof(long)) > +/* e.g. BIT_RANGE(15, 0) -> 0xff00 */ > +#define BIT_RANGE(hb, lb) ((2ull << (hb)) - (1ull << (lb)))
Isn't this undefined behaviour if the hb is 63? Also there is semantic overlap with the MAKE_64BIT_MASK macro proposed in https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg02154.html (which also has ub, but see https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg02614.html for the version which doesn't). I prefer a "start, length" macro to "position, position", because this matches what we already have for the deposit and extract functions in this header. thanks -- PMM
