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RE: Denormal input handling
From: |
Michael Morrell |
Subject: |
RE: Denormal input handling |
Date: |
Tue, 22 Jun 2021 00:57:26 +0000 |
Richard,
I was under the mistaken impression that your changes in this area (splitting
float_flag_input_denormal into 2 flags) were already checked in, but I see now
that is not the case. I should probably wait until that is done before I try
to claim there are additional issues here.
Michael
-----Original Message-----
From: Richard Henderson <richard.henderson@linaro.org>
Sent: Monday, June 21, 2021 4:30 PM
To: Michael Morrell <mmorrell@tachyum.com>; qemu-devel@nongnu.org
Subject: Re: Denormal input handling
On 6/21/21 4:13 PM, Michael Morrell wrote:
> I have another couple of thoughts around input denormal handling.
>
> The first is straightforward. I noticed that the Aarch64 port doesn't
> report input denormals (I could not find any code which sets the IDC
> bit in the FPSR). I found code in the arm (not aarch64) port that
> sets other bits like IXC, but nothing for IDC. Is that simply because no
> one has bothered to add this support?
It's because we failed to use symbolic constants. See
vfp_exceptbits_from_host. Which
*is* used for both aarch64 and arm.
> The second concerns support for cases where multiple exception conditions
> occur. I had
> originally thought that denormal input handling would be orthogonal to
> everything else and
> so a case like "sNaN + denorm" would set both the invalid and input denormal
> flags or
> "denorm / 0" would set both idivde by zero and input denormal, but I don't
> think that is
> true for at least some architectures. Perhaps some specialization is needed
> here?
If you've got a specific example, we can look at it. There's no point adding
specialization that isn't going to be used.
r~