* ntohs/ntohl and bitops
@ 2006-01-10 22:02 Ulrich Drepper
2006-01-11 8:00 ` David S. Miller
0 siblings, 1 reply; 13+ messages in thread
From: Ulrich Drepper @ 2006-01-10 22:02 UTC (permalink / raw)
To: Linux Kernel, David S. Miller
[-- Attachment #1: Type: text/plain, Size: 564 bytes --]
I just saw this in a patch:
+ if (ntohs(ih->frag_off) & IP_OFFSET)
+ return EBT_NOMATCH;
This isn't optimal, it requires a byte switch little endian machines.
The compiler isn't smart enough. It would be better to use
if (ih->frag_off & ntohs(IP_OFFSET))
where the byte-swap can be done at compile time. This is kind of ugly,
I guess, so maybe a dedicate macro
net_host_bit_p(ih->frag_off, IP_OFFSET)
??
--
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-10 22:02 ntohs/ntohl and bitops Ulrich Drepper
@ 2006-01-11 8:00 ` David S. Miller
2006-01-11 8:13 ` Arjan van de Ven
2006-01-12 1:04 ` Pavel Machek
0 siblings, 2 replies; 13+ messages in thread
From: David S. Miller @ 2006-01-11 8:00 UTC (permalink / raw)
To: drepper; +Cc: linux-kernel
From: Ulrich Drepper <drepper@redhat.com>
Date: Tue, 10 Jan 2006 14:02:52 -0800
> I just saw this in a patch:
>
> + if (ntohs(ih->frag_off) & IP_OFFSET)
> + return EBT_NOMATCH;
>
> This isn't optimal, it requires a byte switch little endian machines.
> The compiler isn't smart enough. It would be better to use
>
> if (ih->frag_off & ntohs(IP_OFFSET))
>
> where the byte-swap can be done at compile time. This is kind of ugly,
> I guess, so maybe a dedicate macro
>
> net_host_bit_p(ih->frag_off, IP_OFFSET)
The first suggestion isn't considered ugly, and the best form is:
if (ih->frag_off & __constant_htons(IP_OFFSET))
I'll fix that up when I get a chance, thanks for catching it Uli.
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 8:00 ` David S. Miller
@ 2006-01-11 8:13 ` Arjan van de Ven
2006-01-11 8:36 ` David S. Miller
2006-01-11 8:36 ` Ulrich Drepper
2006-01-12 1:04 ` Pavel Machek
1 sibling, 2 replies; 13+ messages in thread
From: Arjan van de Ven @ 2006-01-11 8:13 UTC (permalink / raw)
To: David S. Miller; +Cc: drepper, linux-kernel
On Wed, 2006-01-11 at 00:00 -0800, David S. Miller wrote:
> From: Ulrich Drepper <drepper@redhat.com>
> Date: Tue, 10 Jan 2006 14:02:52 -0800
>
> > I just saw this in a patch:
> >
> > + if (ntohs(ih->frag_off) & IP_OFFSET)
> > + return EBT_NOMATCH;
> >
> > This isn't optimal, it requires a byte switch little endian machines.
> > The compiler isn't smart enough. It would be better to use
> >
> > if (ih->frag_off & ntohs(IP_OFFSET))
> >
> > where the byte-swap can be done at compile time. This is kind of ugly,
> > I guess, so maybe a dedicate macro
> >
> > net_host_bit_p(ih->frag_off, IP_OFFSET)
>
> The first suggestion isn't considered ugly, and the best form is:
>
> if (ih->frag_off & __constant_htons(IP_OFFSET))
why this __constant_htons and not just plain htons ??
htons() gets auto-remapped to that anyway via the builtin "is this a
constant" thing...... and to be honest htons() is more readable.
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 8:13 ` Arjan van de Ven
@ 2006-01-11 8:36 ` David S. Miller
2006-01-11 8:36 ` Ulrich Drepper
1 sibling, 0 replies; 13+ messages in thread
From: David S. Miller @ 2006-01-11 8:36 UTC (permalink / raw)
To: arjan; +Cc: drepper, linux-kernel
From: Arjan van de Ven <arjan@infradead.org>
Date: Wed, 11 Jan 2006 09:13:11 +0100
> > The first suggestion isn't considered ugly, and the best form is:
> >
> > if (ih->frag_off & __constant_htons(IP_OFFSET))
>
> why this __constant_htons and not just plain htons ??
> htons() gets auto-remapped to that anyway via the builtin "is this a
> constant" thing...... and to be honest htons() is more readable.
You're right.
We use the __constant_*() things for structure initialization
which needs to be compile time.
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 8:13 ` Arjan van de Ven
2006-01-11 8:36 ` David S. Miller
@ 2006-01-11 8:36 ` Ulrich Drepper
2006-01-11 8:44 ` David S. Miller
1 sibling, 1 reply; 13+ messages in thread
From: Ulrich Drepper @ 2006-01-11 8:36 UTC (permalink / raw)
To: Arjan van de Ven; +Cc: David S. Miller, linux-kernel
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Arjan van de Ven wrote:
> why this __constant_htons and not just plain htons ??
> htons() gets auto-remapped to that anyway via the builtin "is this a
> constant" thing...... and to be honest htons() is more readable.
Indeed, why the need for the uglification?
Anyway, candidates for this kind of transformation:
net/ipx/af_ipx.c:1450: if (ntohs(addr->sipx_port) <
IPX_MIN_EPHEMERAL_SOCKET &&
net/atm/br2684.c:308: if (ntohs(eth->h_proto) >= 1536)
net/ipv6/netfilter/ip6t_LOG.c:114: if
(ntohs(fh->frag_off) & 0xFFF8)
net/ipv6/exthdrs_core.c:89: if (ntohs(*fp) & ~0x7)
net/ipv4/ipmr.c:1182: if (skb->len+encap > dst_mtu(&rt->u.dst) &&
(ntohs(iph->frag_off) & IP_DF)) {
net/ipv4/netfilter/ip_conntrack_helper_pptp.c:710: if
(ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
net/ipv4/netfilter/ipt_LOG.c:70: if (ntohs(ih->frag_off) & IP_CE)
net/ipv4/netfilter/ipt_LOG.c:72: if (ntohs(ih->frag_off) & IP_DF)
net/ipv4/netfilter/ipt_LOG.c:74: if (ntohs(ih->frag_off) & IP_MF)
net/ipv4/netfilter/ipt_LOG.c:78: if (ntohs(ih->frag_off) & IP_OFFSET)
net/ipv4/netfilter/ipt_LOG.c:108: if (ntohs(ih->frag_off)
& IP_OFFSET)
net/ipv4/netfilter/ipt_LOG.c:180: if (ntohs(ih->frag_off)
& IP_OFFSET)
net/ipv4/netfilter/ipt_LOG.c:221: if (ntohs(ih->frag_off)
& IP_OFFSET)
net/ipv4/netfilter/ipt_LOG.c:286: if (ntohs(ih->frag_off)
& IP_OFFSET)
net/ipv4/netfilter/ipt_LOG.c:311: if (ntohs(ih->frag_off)
& IP_OFFSET)
net/bridge/netfilter/ebt_ip.c:55: if (ntohs(ih->frag_off)
& IP_OFFSET)
net/sunrpc/auth_gss/svcauth_gss.c:793: if (ntohl(svc_getu32(argv)) !=
RPC_GSS_VERSION)
net/sunrpc/auth_gss/svcauth_gss.c:823: if
(ntohl(svc_getu32(argv)) != RPC_AUTH_NULL)
net/sunrpc/auth_gss/svcauth_gss.c:825: if
(ntohl(svc_getu32(argv)) != 0)
net/bluetooth/bnep/core.c:343: if (ntohs(s->eh.h_proto) == 0x8100) {
(svcauth_gss.c:825 is a good one).
For consistency reasons, ntohs should be changed to htons here:
net/ipv6/netfilter/ip6t_eui64.c:43: if (eth_hdr(skb)->h_proto ==
ntohs(ETH_P_IPV6)) {
Around net/ipv4/ipconfig.c:376 you might want to store the transformed
ic_myaddr in a variable instead of repeating the ntohl call.
--
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 8:36 ` Ulrich Drepper
@ 2006-01-11 8:44 ` David S. Miller
2006-01-11 9:48 ` Jakub Jelinek
0 siblings, 1 reply; 13+ messages in thread
From: David S. Miller @ 2006-01-11 8:44 UTC (permalink / raw)
To: drepper; +Cc: arjan, linux-kernel
From: Ulrich Drepper <drepper@redhat.com>
Date: Wed, 11 Jan 2006 00:36:11 -0800
> Anyway, candidates for this kind of transformation:
>
> net/ipx/af_ipx.c:1450: if (ntohs(addr->sipx_port) <
> IPX_MIN_EPHEMERAL_SOCKET &&
Does it work for comparisons? F.e.:
if (val < ntohs(VAL))
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 8:44 ` David S. Miller
@ 2006-01-11 9:48 ` Jakub Jelinek
2006-01-11 18:35 ` Jan Engelhardt
0 siblings, 1 reply; 13+ messages in thread
From: Jakub Jelinek @ 2006-01-11 9:48 UTC (permalink / raw)
To: David S. Miller; +Cc: drepper, arjan, linux-kernel
On Wed, Jan 11, 2006 at 12:44:18AM -0800, David S. Miller wrote:
> From: Ulrich Drepper <drepper@redhat.com>
> Date: Wed, 11 Jan 2006 00:36:11 -0800
>
> > Anyway, candidates for this kind of transformation:
> >
> > net/ipx/af_ipx.c:1450: if (ntohs(addr->sipx_port) <
> > IPX_MIN_EPHEMERAL_SOCKET &&
>
> Does it work for comparisons? F.e.:
>
> if (val < ntohs(VAL))
No, only for ==, !=, &, |, ~.
Jakub
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 9:48 ` Jakub Jelinek
@ 2006-01-11 18:35 ` Jan Engelhardt
2006-01-11 18:45 ` Ulrich Drepper
0 siblings, 1 reply; 13+ messages in thread
From: Jan Engelhardt @ 2006-01-11 18:35 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: David S. Miller, drepper, arjan, linux-kernel
>> Does it work for comparisons? F.e.:
>>
>> if (val < ntohs(VAL))
>
>No, only for ==, !=, &, |, ~.
And ^?
Jan Engelhardt
--
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 18:35 ` Jan Engelhardt
@ 2006-01-11 18:45 ` Ulrich Drepper
2006-01-11 20:19 ` David S. Miller
0 siblings, 1 reply; 13+ messages in thread
From: Ulrich Drepper @ 2006-01-11 18:45 UTC (permalink / raw)
To: Jan Engelhardt; +Cc: Jakub Jelinek, David S. Miller, arjan, linux-kernel
[-- Attachment #1: Type: text/plain, Size: 431 bytes --]
Jan Engelhardt wrote:
> And ^?
^ is fine.
And just to be complete: I sent DaveM the correct line for that file in
question, I just C&Ped the wrong line my scripts produced. The mail
seem not to make it to lkml. In fact, none of my mail originated from
the gmail account ever made it. I don't know what filter doesn't like me.
--
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 18:45 ` Ulrich Drepper
@ 2006-01-11 20:19 ` David S. Miller
0 siblings, 0 replies; 13+ messages in thread
From: David S. Miller @ 2006-01-11 20:19 UTC (permalink / raw)
To: drepper; +Cc: jengelh, jakub, arjan, linux-kernel
From: Ulrich Drepper <drepper@redhat.com>
Date: Wed, 11 Jan 2006 10:45:00 -0800
> And just to be complete: I sent DaveM the correct line for that file in
> question, I just C&Ped the wrong line my scripts produced. The mail
> seem not to make it to lkml. In fact, none of my mail originated from
> the gmail account ever made it. I don't know what filter doesn't like me.
This one:
m/^Content-Transfer-Encoding:\s*base64/i
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-11 8:00 ` David S. Miller
2006-01-11 8:13 ` Arjan van de Ven
@ 2006-01-12 1:04 ` Pavel Machek
2006-01-14 9:52 ` YOSHIFUJI Hideaki / 吉藤英明
2006-01-15 1:46 ` David S. Miller
1 sibling, 2 replies; 13+ messages in thread
From: Pavel Machek @ 2006-01-12 1:04 UTC (permalink / raw)
To: David S. Miller; +Cc: drepper, linux-kernel
On Wed 11-01-06 00:00:20, David S. Miller wrote:
> From: Ulrich Drepper <drepper@redhat.com>
> Date: Tue, 10 Jan 2006 14:02:52 -0800
>
> > I just saw this in a patch:
> >
> > + if (ntohs(ih->frag_off) & IP_OFFSET)
> > + return EBT_NOMATCH;
> >
> > This isn't optimal, it requires a byte switch little endian machines.
> > The compiler isn't smart enough. It would be better to use
> >
> > if (ih->frag_off & ntohs(IP_OFFSET))
> >
> > where the byte-swap can be done at compile time. This is kind of ugly,
> > I guess, so maybe a dedicate macro
> >
> > net_host_bit_p(ih->frag_off, IP_OFFSET)
>
> The first suggestion isn't considered ugly, and the best form is:
>
> if (ih->frag_off & __constant_htons(IP_OFFSET))
>
> I'll fix that up when I get a chance, thanks for catching it Uli.
Could you possibly
#define IP_OFFSET htons(1234)
?
Noone should need it in native endianity, no?
--
Thanks, Sharp!
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-12 1:04 ` Pavel Machek
@ 2006-01-14 9:52 ` YOSHIFUJI Hideaki / 吉藤英明
2006-01-15 1:46 ` David S. Miller
1 sibling, 0 replies; 13+ messages in thread
From: YOSHIFUJI Hideaki / 吉藤英明 @ 2006-01-14 9:52 UTC (permalink / raw)
To: pavel; +Cc: davem, drepper, linux-kernel, yoshfuji
In article <20060112010406.GA2367@ucw.cz> (at Thu, 12 Jan 2006 01:04:06 +0000), Pavel Machek <pavel@ucw.cz> says:
>
> On Wed 11-01-06 00:00:20, David S. Miller wrote:
> > From: Ulrich Drepper <drepper@redhat.com>
> > Date: Tue, 10 Jan 2006 14:02:52 -0800
> >
> > > I just saw this in a patch:
> > >
> > > + if (ntohs(ih->frag_off) & IP_OFFSET)
> > > + return EBT_NOMATCH;
> > >
> > > This isn't optimal, it requires a byte switch little endian machines.
> > > The compiler isn't smart enough. It would be better to use
> > >
> > > if (ih->frag_off & ntohs(IP_OFFSET))
:
> Could you possibly
> #define IP_OFFSET htons(1234)
> ?
In this case, you should use __constant_htons().
I still prefer:
if (ih->frag_off & htons(IP_OFFSET))
though.
--yoshfuji
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: ntohs/ntohl and bitops
2006-01-12 1:04 ` Pavel Machek
2006-01-14 9:52 ` YOSHIFUJI Hideaki / 吉藤英明
@ 2006-01-15 1:46 ` David S. Miller
1 sibling, 0 replies; 13+ messages in thread
From: David S. Miller @ 2006-01-15 1:46 UTC (permalink / raw)
To: pavel; +Cc: drepper, linux-kernel
From: Pavel Machek <pavel@ucw.cz>
Date: Thu, 12 Jan 2006 01:04:06 +0000
> Could you possibly
> #define IP_OFFSET htons(1234)
> ?
>
> Noone should need it in native endianity, no?
That's definitely going to be error prone.
And I bet the BSD headers define it in cpu endainness
as well.
^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2006-01-15 1:50 UTC | newest]
Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2006-01-10 22:02 ntohs/ntohl and bitops Ulrich Drepper
2006-01-11 8:00 ` David S. Miller
2006-01-11 8:13 ` Arjan van de Ven
2006-01-11 8:36 ` David S. Miller
2006-01-11 8:36 ` Ulrich Drepper
2006-01-11 8:44 ` David S. Miller
2006-01-11 9:48 ` Jakub Jelinek
2006-01-11 18:35 ` Jan Engelhardt
2006-01-11 18:45 ` Ulrich Drepper
2006-01-11 20:19 ` David S. Miller
2006-01-12 1:04 ` Pavel Machek
2006-01-14 9:52 ` YOSHIFUJI Hideaki / 吉藤英明
2006-01-15 1:46 ` David S. Miller
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