From: Al Viro <viro@ZenIV.linux.org.uk>
To: Richard Henderson <rth@twiddle.net>
Cc: Peter Maydell <peter.maydell@linaro.org>,
QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions
Date: Thu, 3 Jul 2014 23:47:04 +0100 [thread overview]
Message-ID: <20140703224704.GR18016@ZenIV.linux.org.uk> (raw)
In-Reply-To: <53B5BAC7.1010603@twiddle.net>
On Thu, Jul 03, 2014 at 01:19:19PM -0700, Richard Henderson wrote:
> > Grr... Wrong check, obviously - we want to check that tmp + MSB(tmp2) is 0.
> > Something like
> > setcond_32 tmp2, tmp2, zero, TCG_COND_LT
> > add_i32 tmp, tmp2, tmp
> > call helper_IOV_if_not_zero tmp
> > for 32bit ones and
> > setcond_64 tmp2, vc, zero, TCG_COND_LT
> > add_i64 tmp, tmp2, tmp
> > call helper_IOV_if_not_zero tmp
> > for 64bit ones, or would it be better just to pass both arguments to helper
> > and let it deal with the check? I'm not familiar enough with TCG, sorry...
> >
>
> I believe I have a tidy solution to these /v insns. New patch set shortly.
Hmm...
+ tcg_gen_eqv_i64(tmp, va, vb);
+ tcg_gen_mov_i64(tmp2, va);
+ tcg_gen_add_i64(vc, va, vb);
+ tcg_gen_xor_i64(tmp2, tmp2, vc);
+ tcg_gen_and_i64(tmp, tmp, tmp2);
+ tcg_gen_shri_i64(tmp, tmp, 63);
+ tcg_gen_movi_i64(tmp2, 0);
+ gen_helper_check_overflow(cpu_env, tmp, tmp2);
How can that be correct? Suppose a = b = 0. We get
tcg_gen_eqv_i64(tmp, va, vb); -> tmp = -1
tcg_gen_mov_i64(tmp2, va); -> tmp2 = 0
tcg_gen_add_i64(vc, va, vb); -> c = 0
tcg_gen_xor_i64(tmp2, tmp2, vc);-> tmp2 = 0
tcg_gen_and_i64(tmp, tmp, tmp2);-> tmp = -1
tcg_gen_shri_i64(tmp, tmp, 63); -> tmp = 1
tcg_gen_movi_i64(tmp2, 0); -> tmp2 = 0
gen_helper_check_overflow(cpu_env, tmp, tmp2); -> not equal, overflow.
What am I missing here?
next prev parent reply other threads:[~2014-07-03 22:47 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-24 4:34 [Qemu-devel] [RFC] alpha qemu arithmetic exceptions Al Viro
2014-06-24 16:52 ` Al Viro
2014-06-24 18:33 ` Richard Henderson
2014-06-24 20:32 ` Al Viro
2014-06-24 20:57 ` Richard Henderson
2014-06-24 21:24 ` Al Viro
2014-06-24 21:32 ` Richard Henderson
2014-06-25 7:01 ` Al Viro
2014-06-25 9:27 ` Peter Maydell
2014-06-25 14:26 ` Al Viro
2014-06-25 17:41 ` Peter Maydell
2014-06-26 5:55 ` Al Viro
2014-06-30 18:39 ` Richard Henderson
2014-06-30 20:56 ` Al Viro
2014-07-01 4:34 ` Al Viro
2014-07-01 5:00 ` Al Viro
2014-07-01 14:31 ` Richard Henderson
2014-07-01 17:03 ` Richard Henderson
2014-07-01 17:50 ` Al Viro
2014-07-01 18:23 ` Peter Maydell
2014-07-01 18:30 ` Richard Henderson
2014-07-01 19:08 ` Peter Maydell
2014-07-02 4:05 ` Al Viro
2014-07-02 5:50 ` Al Viro
2014-07-02 6:17 ` Al Viro
2014-07-02 15:26 ` Richard Henderson
2014-07-02 15:49 ` Al Viro
2014-07-02 14:59 ` Richard Henderson
2014-07-02 15:20 ` Al Viro
2014-07-03 6:51 ` Al Viro
2014-07-03 18:25 ` Al Viro
2014-07-03 20:19 ` Richard Henderson
2014-07-03 22:47 ` Al Viro [this message]
2014-07-03 23:05 ` Peter Maydell
2014-07-03 23:22 ` Al Viro
2014-07-04 0:50 ` Al Viro
2014-07-04 4:30 ` Richard Henderson
2014-07-04 7:29 ` Al Viro
2014-07-05 1:40 ` Al Viro
2014-07-05 5:26 ` Al Viro
2014-07-05 21:09 ` Al Viro
2014-07-05 22:55 ` Al Viro
2014-07-07 14:11 ` Richard Henderson
2014-07-07 15:06 ` Al Viro
2014-07-07 16:20 ` Richard Henderson
2014-07-08 4:20 ` Al Viro
2014-07-08 6:03 ` Richard Henderson
2014-07-08 6:54 ` Al Viro
2014-07-08 7:13 ` Al Viro
2014-07-08 8:05 ` Peter Maydell
2014-07-08 14:53 ` Richard Henderson
2014-07-08 16:13 ` Al Viro
2014-07-08 16:33 ` Peter Maydell
2014-07-08 17:20 ` Al Viro
2014-07-08 19:32 ` Peter Maydell
2014-07-08 20:12 ` Al Viro
2014-07-09 9:19 ` Alex Bennée
2014-07-09 9:04 ` Alex Bennée
2014-07-08 18:12 ` Richard Henderson
2014-07-08 19:02 ` Al Viro
2014-07-08 19:04 ` Richard Henderson
2014-07-08 20:20 ` Al Viro
2014-07-09 4:59 ` Richard Henderson
2014-07-09 5:47 ` Al Viro
2014-07-09 15:14 ` Richard Henderson
2014-07-09 16:41 ` Al Viro
2014-06-24 18:23 ` Richard Henderson
2014-06-24 20:47 ` Al Viro
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=20140703224704.GR18016@ZenIV.linux.org.uk \
--to=viro@zeniv.linux.org.uk \
--cc=peter.maydell@linaro.org \
--cc=qemu-devel@nongnu.org \
--cc=rth@twiddle.net \
/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).