On Wed, Oct 01, 2014 at 04:02:36PM -0700, Jarno Rajahalme wrote:
> Depending on the CPU, count_1bits() may be more or less expensive, so
> it is better to avoid unnecessary calls to it. When the map has
> consecutive 1-bits, those can be cleared without counting.
>
> Signed-off-by: Jarno Rajahalme <jrajaha...@nicira.com>
> ---
> lib/flow.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/flow.h b/lib/flow.h
> index 9bb9a58..a6e75c7 100644
> --- a/lib/flow.h
> +++ b/lib/flow.h
> @@ -507,7 +507,8 @@ mf_get_next_in_map(uint64_t *fmap, uint64_t rm1bit, const
> uint32_t **fp,
> *fmap -= trash;
> *fp += count_1bits(trash);
> }
> - *value = **fp;
> + *fmap -= rm1bit;
> + *value = *(*fp)++;
> }
> return rm1bit != 0;
> }
I think that MINIFLOW_FOR_EACH_IN_MAP can be improved in other ways.
rm1bit_ seems unnecessary: it is always rightmost_1bit(map_) at point
of use, so it could be calculated inside mf_get_next_in_map() if &map
were passed in instead. Also, it seems a bit awkward to have
declarations outside the for loop.
What do you think of this version? It incorporates your improvement
but avoids the out-of-for-statement declarations and moves the rm1bit
calculation inside the function. It passes the unit tests for me.
struct mf_for_each_in_map_aux {
const uint32_t *values;
uint64_t fmap;
uint64_t map;
};
static inline bool
mf_get_next_in_map(struct mf_for_each_in_map_aux *aux, uint32_t *value)
{
if (aux->map) {
uint64_t rm1bit = rightmost_1bit(aux->map);
aux->map -= rm1bit;
if (aux->fmap & rm1bit) {
/* Advance 'aux->values' to point to the value for 'rm1bit'. */
uint64_t trash = aux->fmap & (rm1bit - 1);
if (trash) {
aux->fmap -= trash;
aux->values += count_1bits(trash);
}
/* Retrieve the value for 'rm1bit' then advance past it. */
aux->fmap -= rm1bit;
*value = *aux->values++;
} else {
*value = 0;
}
return true;
} else {
return false;
}
}
/* Iterate through all miniflow u32 values specified by 'MAP'. */
#define MINIFLOW_FOR_EACH_IN_MAP(VALUE, FLOW, MAP) \
for (struct mf_for_each_in_map_aux aux__ \
= { miniflow_get_u32_values(FLOW), (FLOW)->map, MAP }; \
mf_get_next_in_map(&aux__, &(VALUE)); \
)
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