* [PATCH 2/4] dsmark: get rid of trivial function
[not found] <20080120130542.16720b45@deepthought>
@ 2008-01-20 21:25 ` Stephen Hemminger
2008-01-21 0:16 ` Patrick McHardy
0 siblings, 1 reply; 6+ messages in thread
From: Stephen Hemminger @ 2008-01-20 21:25 UTC (permalink / raw)
To: David Miller; +Cc: Patrick McHardy, netdev
Replace loop in dsmark_valid_indices with equivalent bit math.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
--- a/net/sched/sch_dsmark.c 2008-01-20 13:07:58.000000000 -0800
+++ b/net/sched/sch_dsmark.c 2008-01-20 13:22:54.000000000 -0800
@@ -45,13 +45,8 @@ struct dsmark_qdisc_data {
static inline int dsmark_valid_indices(u16 indices)
{
- while (indices != 1) {
- if (indices & 1)
- return 0;
- indices >>= 1;
- }
-
- return 1;
+ /* Must have only one bit set */
+ return (indices & (indices - 1)) == 0;
}
static inline int dsmark_valid_index(struct dsmark_qdisc_data *p, u16 index)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 2/4] dsmark: get rid of trivial function
2008-01-20 21:25 ` [PATCH 2/4] dsmark: get rid of trivial function Stephen Hemminger
@ 2008-01-21 0:16 ` Patrick McHardy
2008-01-21 8:39 ` Ilpo Järvinen
2008-01-21 10:22 ` David Miller
0 siblings, 2 replies; 6+ messages in thread
From: Patrick McHardy @ 2008-01-21 0:16 UTC (permalink / raw)
To: Stephen Hemminger; +Cc: David Miller, netdev
Stephen Hemminger wrote:
> Replace loop in dsmark_valid_indices with equivalent bit math.
>
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>
> --- a/net/sched/sch_dsmark.c 2008-01-20 13:07:58.000000000 -0800
> +++ b/net/sched/sch_dsmark.c 2008-01-20 13:22:54.000000000 -0800
> @@ -45,13 +45,8 @@ struct dsmark_qdisc_data {
>
> static inline int dsmark_valid_indices(u16 indices)
> {
> - while (indices != 1) {
> - if (indices & 1)
> - return 0;
> - indices >>= 1;
> - }
> -
> - return 1;
> + /* Must have only one bit set */
> + return (indices & (indices - 1)) == 0;
hweight seems easier to understand, it took me a bit
to realize that the comment matches the code :)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 2/4] dsmark: get rid of trivial function
2008-01-21 0:16 ` Patrick McHardy
@ 2008-01-21 8:39 ` Ilpo Järvinen
2008-01-21 10:22 ` David Miller
1 sibling, 0 replies; 6+ messages in thread
From: Ilpo Järvinen @ 2008-01-21 8:39 UTC (permalink / raw)
To: Patrick McHardy, Stephen Hemminger; +Cc: David Miller, Netdev
On Mon, 21 Jan 2008, Patrick McHardy wrote:
> Stephen Hemminger wrote:
> > Replace loop in dsmark_valid_indices with equivalent bit math.
> >
> > Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> >
> > --- a/net/sched/sch_dsmark.c 2008-01-20 13:07:58.000000000 -0800
> > +++ b/net/sched/sch_dsmark.c 2008-01-20 13:22:54.000000000 -0800
> > @@ -45,13 +45,8 @@ struct dsmark_qdisc_data {
> >
> > static inline int dsmark_valid_indices(u16 indices)
> > {
> > - while (indices != 1) {
> > - if (indices & 1)
> > - return 0;
> > - indices >>= 1;
> > - }
> > -
> > - return 1;
> > + /* Must have only one bit set */
> > + return (indices & (indices - 1)) == 0;
Isn't there some magic under include/linux to do that btw, I suppose
that if the caller side zero check is pushed down there too, the
is_power_of_2() is 100% match? :-)
> hweight seems easier to understand, it took me a bit
> to realize that the comment matches the code :)
In addition, the original seems infinite loop with zero indices given
but luckily that was checked at the caller site already...
--
i.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 2/4] dsmark: get rid of trivial function
2008-01-21 0:16 ` Patrick McHardy
2008-01-21 8:39 ` Ilpo Järvinen
@ 2008-01-21 10:22 ` David Miller
2008-01-22 3:47 ` Stephen Hemminger
1 sibling, 1 reply; 6+ messages in thread
From: David Miller @ 2008-01-21 10:22 UTC (permalink / raw)
To: kaber; +Cc: shemminger, netdev
From: Patrick McHardy <kaber@trash.net>
Date: Mon, 21 Jan 2008 01:16:32 +0100
> Stephen Hemminger wrote:
> > Replace loop in dsmark_valid_indices with equivalent bit math.
> >
> > Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> >
> > --- a/net/sched/sch_dsmark.c 2008-01-20 13:07:58.000000000 -0800
> > +++ b/net/sched/sch_dsmark.c 2008-01-20 13:22:54.000000000 -0800
> > @@ -45,13 +45,8 @@ struct dsmark_qdisc_data {
> >
> > static inline int dsmark_valid_indices(u16 indices)
> > {
> > - while (indices != 1) {
> > - if (indices & 1)
> > - return 0;
> > - indices >>= 1;
> > - }
> > -
> > - return 1;
> > + /* Must have only one bit set */
> > + return (indices & (indices - 1)) == 0;
>
> hweight seems easier to understand, it took me a bit
> to realize that the comment matches the code :)
Sounds good. Here is what I ended up checking in.
[PKT_SCHED] dsmark: Use hweight32() instead of convoluted loop.
Based upon a patch by Stephen Hemminger and suggestions
from Patrick McHardy.
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/sch_dsmark.c b/net/sched/sch_dsmark.c
index a9732ae..d96eaf0 100644
--- a/net/sched/sch_dsmark.c
+++ b/net/sched/sch_dsmark.c
@@ -10,6 +10,7 @@
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
+#include <linux/bitops.h>
#include <net/pkt_sched.h>
#include <net/dsfield.h>
#include <net/inet_ecn.h>
@@ -43,17 +44,6 @@ struct dsmark_qdisc_data {
int set_tc_index;
};
-static inline int dsmark_valid_indices(u16 indices)
-{
- while (indices != 1) {
- if (indices & 1)
- return 0;
- indices >>= 1;
- }
-
- return 1;
-}
-
static inline int dsmark_valid_index(struct dsmark_qdisc_data *p, u16 index)
{
return (index <= p->indices && index > 0);
@@ -348,7 +338,8 @@ static int dsmark_init(struct Qdisc *sch, struct rtattr *opt)
goto errout;
indices = RTA_GET_U16(tb[TCA_DSMARK_INDICES-1]);
- if (!indices || !dsmark_valid_indices(indices))
+
+ if (hweight32(indices) != 1)
goto errout;
if (tb[TCA_DSMARK_DEFAULT_INDEX-1])
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 2/4] dsmark: get rid of trivial function
2008-01-21 10:22 ` David Miller
@ 2008-01-22 3:47 ` Stephen Hemminger
2008-01-22 3:59 ` David Miller
0 siblings, 1 reply; 6+ messages in thread
From: Stephen Hemminger @ 2008-01-22 3:47 UTC (permalink / raw)
To: David Miller; +Cc: netdev
On Mon, 21 Jan 2008 02:22:23 -0800 (PST)
David Miller <davem@davemloft.net> wrote:
> From: Patrick McHardy <kaber@trash.net>
> Date: Mon, 21 Jan 2008 01:16:32 +0100
>
> > Stephen Hemminger wrote:
> > > Replace loop in dsmark_valid_indices with equivalent bit math.
> > >
> > > Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> > >
> > > --- a/net/sched/sch_dsmark.c 2008-01-20 13:07:58.000000000 -0800
> > > +++ b/net/sched/sch_dsmark.c 2008-01-20 13:22:54.000000000 -0800
> > > @@ -45,13 +45,8 @@ struct dsmark_qdisc_data {
> > >
> > > static inline int dsmark_valid_indices(u16 indices)
> > > {
> > > - while (indices != 1) {
> > > - if (indices & 1)
> > > - return 0;
> > > - indices >>= 1;
> > > - }
> > > -
> > > - return 1;
> > > + /* Must have only one bit set */
> > > + return (indices & (indices - 1)) == 0;
> >
> > hweight seems easier to understand, it took me a bit
> > to realize that the comment matches the code :)
>
> Sounds good. Here is what I ended up checking in.
>
> [PKT_SCHED] dsmark: Use hweight32() instead of convoluted loop.
>
> Based upon a patch by Stephen Hemminger and suggestions
> from Patrick McHardy.
>
> Signed-off-by: David S. Miller <davem@davemloft.net>
>
> diff --git a/net/sched/sch_dsmark.c b/net/sched/sch_dsmark.c
> index a9732ae..d96eaf0 100644
> --- a/net/sched/sch_dsmark.c
> +++ b/net/sched/sch_dsmark.c
> @@ -10,6 +10,7 @@
> #include <linux/errno.h>
> #include <linux/skbuff.h>
> #include <linux/rtnetlink.h>
> +#include <linux/bitops.h>
> #include <net/pkt_sched.h>
> #include <net/dsfield.h>
> #include <net/inet_ecn.h>
> @@ -43,17 +44,6 @@ struct dsmark_qdisc_data {
> int set_tc_index;
> };
>
> -static inline int dsmark_valid_indices(u16 indices)
> -{
> - while (indices != 1) {
> - if (indices & 1)
> - return 0;
> - indices >>= 1;
> - }
> -
> - return 1;
> -}
> -
> static inline int dsmark_valid_index(struct dsmark_qdisc_data *p, u16 index)
> {
> return (index <= p->indices && index > 0);
> @@ -348,7 +338,8 @@ static int dsmark_init(struct Qdisc *sch, struct rtattr *opt)
> goto errout;
>
> indices = RTA_GET_U16(tb[TCA_DSMARK_INDICES-1]);
> - if (!indices || !dsmark_valid_indices(indices))
> +
> + if (hweight32(indices) != 1)
> goto errout;
Come on Dave, that is a step backwards.
So you took a two instruction thing that any programmer who ever had one of those
technical trick interviews would surely understand, and made it call a function...
Seems like the thing you would consul others against.
Please use !is_power_of_2(indices) instead.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 2/4] dsmark: get rid of trivial function
2008-01-22 3:47 ` Stephen Hemminger
@ 2008-01-22 3:59 ` David Miller
0 siblings, 0 replies; 6+ messages in thread
From: David Miller @ 2008-01-22 3:59 UTC (permalink / raw)
To: stephen.hemminger; +Cc: netdev
From: Stephen Hemminger <stephen.hemminger@vyatta.com>
Date: Mon, 21 Jan 2008 19:47:51 -0800
> >
> > indices = RTA_GET_U16(tb[TCA_DSMARK_INDICES-1]);
> > - if (!indices || !dsmark_valid_indices(indices))
> > +
> > + if (hweight32(indices) != 1)
> > goto errout;
>
> Come on Dave, that is a step backwards.
Absolutely not.
> So you took a two instruction thing that any programmer who ever had
> one of those technical trick interviews would surely understand, and
> made it call a function... Seems like the thing you would consul
> others against.
It's counting bits, "hamming weight" is a count of bits.
That is more understandable to me than:
Oh BTW, power of two values also just so happen to
have only 1 bit set.
Testing for a power of two obfuscates the meaning of the
test. It doesn't want a power-of-two, it wants a bitmask
with only one bit set.
^ permalink raw reply [flat|nested] 6+ messages in thread
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[not found] <20080120130542.16720b45@deepthought>
2008-01-20 21:25 ` [PATCH 2/4] dsmark: get rid of trivial function Stephen Hemminger
2008-01-21 0:16 ` Patrick McHardy
2008-01-21 8:39 ` Ilpo Järvinen
2008-01-21 10:22 ` David Miller
2008-01-22 3:47 ` Stephen Hemminger
2008-01-22 3:59 ` David Miller
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