[ovs-dev] [PATCH 07/17] util: New function bitwise_scan().

[YAMAMOTO Takashi]

> 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 <blp at 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.

Acked-by: YAMAMOTO Takashi <yamamoto at valinux.co.jp>