On Wed, Sep 24, 2014 at 10:33:21AM +0900, YAMAMOTO Takashi wrote:
> > This will acquire its first user in an upcoming commit.
> >
> > This implementation is not optimized at all but it doesn't matter for the
> > purpose for which I intend to initially use it.
> >
> > Signed-off-by: Ben Pfaff <b...@nicira.com>
> > ---
> > lib/util.c | 29 +++++++++++++++++++++++++++++
> > lib/util.h | 2 ++
> > 2 files changed, 31 insertions(+)
> >
> > diff --git a/lib/util.c b/lib/util.c
> > index f3e47b1..01e8a0e 100644
> > --- a/lib/util.c
> > +++ b/lib/util.c
> > @@ -1273,6 +1273,35 @@ bitwise_is_all_zeros(const void *p_, unsigned int
> > len, unsigned int ofs,
> > return true;
> > }
> >
> > +/* Scans the bits in 'p' that have bit offsets 'start' through 'end'
> > + * (inclusive) for the first bit with value 'target'. If one is found,
> > returns
> > + * its offset, otherwise 'end'. 'p' is 'len' bytes long.
> > + *
> > + * If you consider all of 'p' to be a single unsigned integer in network
> > byte
> > + * order, then bit N is the bit with value 2**N. That is, bit 0 is the bit
> > + * with value 1 in p[len - 1], bit 1 is the bit with value 2, bit 2 is the
> > bit
> > + * with value 4, ..., bit 8 is the bit with value 1 in p[len - 2], and so
> > on.
> > + *
> > + * Required invariant:
> > + * start <= end
> > + */
> > +unsigned int
> > +bitwise_scan(const void *p_, unsigned int len, bool target, unsigned int
> > start,
> > + unsigned int end)
> > +{
> > + const uint8_t *p = p_;
> > + unsigned int ofs;
> > +
> > + for (ofs = start; ofs < end; ofs++) {
> > + bool bit = (p[len - (ofs / 8 + 1)] & (1u << (ofs % 8))) != 0;
>
> != 0 seems redundant because converting to c99 bool has the same semantics.
> otherwise looks good to me.
I agree it's redundant. I tend to include this kind of thing anyway
in case OVS ever gets ported to a compiler that lacks C99 bool. With
such a compiler, one usually typedefs bool to char, and conversion to
char will lose any 1-bit above bits 0...7, which could cause really
subtle problems. And with a compiler that does have C99 bool, I
imagine that the extra != 0 is harmless.
Oh, I see that I even mentioned this in CodingStyle:
* bool and <stdbool.h>, but don't assume that bool or _Bool can
only take on the values 0 or 1, because this behavior can't be
simulated on C89 compilers.
> Acked-by: YAMAMOTO Takashi <yamam...@valinux.co.jp>
Thanks!
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