From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: z constraint in powerpc inline assembly ?
Date: Thu, 16 Jan 2020 08:01:01 -0600 [thread overview]
Message-ID: <20200116140101.GQ3191@gate.crashing.org> (raw)
In-Reply-To: <d72263a1-fe17-3192-6930-35ec8394c699@c-s.fr>
Hi!
On Thu, Jan 16, 2020 at 07:11:36AM +0100, Christophe Leroy wrote:
> I'm trying to see if we could enhance TCP checksum calculations by
> splitting inline assembly blocks to give GCC the opportunity to mix it
> with other stuff, but I'm getting difficulties with the carry.
>
> As far as I can read in the documentation, the z constraint represents
> '‘XER[CA]’ carry bit (part of the XER register)'
>
> I've tried the following, but I get errors. Can you help ?
>
> unsigned long cksum(unsigned long a, unsigned long b, unsigned long c)
> {
> unsigned long sum;
> unsigned long carry;
>
> asm("addc %0, %2, %3" : "=r"(sum), "=z"(carry) : "r"(a), "r"(b));
> asm("adde %0, %0, %2" : "+r"(sum), "+z"(carry) : "r"(c));
> asm("addze %0, %0" : "+r"(sum) : "z"(carry));
>
> return sum;
> }
The only register allowed by "z" is a fixed register. You cannot use "z"
in inline asm.
Just write this as C? It should do a reasonable job of it. If you want
*good* code, you need to write it in *actual* assembler code, anyway (hand
scheduled and everything).
Segher
next prev parent reply other threads:[~2020-01-16 14:03 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 6:11 z constraint in powerpc inline assembly ? Christophe Leroy
2020-01-16 8:06 ` Gabriel Paubert
2020-01-16 13:57 ` Segher Boessenkool
2020-01-16 17:42 ` [PosibleSpam] " Gabriel Paubert
2020-01-16 14:01 ` Segher Boessenkool [this message]
2020-01-16 15:54 ` David Laight
2020-01-16 16:21 ` Segher Boessenkool
2020-01-16 16:52 ` David Laight
2020-01-16 17:10 ` Christophe Leroy
2020-01-16 17:20 ` David Laight
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200116140101.GQ3191@gate.crashing.org \
--to=segher@kernel.crashing.org \
--cc=christophe.leroy@c-s.fr \
--cc=linuxppc-dev@lists.ozlabs.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).