From: Richard Henderson <richard.henderson@linaro.org>
To: Stafford Horne <shorne@gmail.com>
Cc: QEMU Development <qemu-devel@nongnu.org>,
Linux OpenRISC <linux-openrisc@vger.kernel.org>
Subject: Re: [PATCH 3/3] target/openrisc: Setup FPU for detecting tininess before rounding
Date: Wed, 3 May 2023 10:41:42 +0100 [thread overview]
Message-ID: <e3fabb1d-7bf6-f251-9649-5a813b409200@linaro.org> (raw)
In-Reply-To: <ZFIl6db3isktCOk8@antec>
On 5/3/23 10:14, Stafford Horne wrote:
>>> + set_default_nan_mode(1, &cpu->env.fp_status);
>>> + set_float_detect_tininess(float_tininess_before_rounding,
>>> + &cpu->env.fp_status);
>>
>> You don't mention the nan change in the commit message.
>
> Right, and I am not sure I need it. Let me remove it and run tests again. I
> was just adding it as a few other architectures did who set
> float_tininess_before_rounding.
What that does is *not* propagate NaN payloads from (some) input to the output. This is
certainly true of RISC-V, which specifies this in their architecture manual. OpenRISC
does not specify any NaN behaviour at all.
It's not a bad choice, really, and it almost certainly simplifies the design of the FPU,
as you can do NaN propagation and silencing in one step.
r~
next prev parent reply other threads:[~2023-05-03 9:41 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-02 18:57 [PATCH 0/3] OpenRISC updates for user space FPU Stafford Horne
2023-05-02 18:57 ` [PATCH 1/3] target/openrisc: Allow fpcsr access in user mode Stafford Horne
2023-05-03 6:29 ` Stafford Horne
2023-05-02 18:57 ` [PATCH 2/3] target/openrisc: Set PC to cpu state on FPU exception Stafford Horne
2023-05-03 7:36 ` Richard Henderson
2023-05-03 9:12 ` Stafford Horne
2023-05-02 18:57 ` [PATCH 3/3] target/openrisc: Setup FPU for detecting tininess before rounding Stafford Horne
2023-05-03 7:37 ` Richard Henderson
2023-05-03 9:14 ` Stafford Horne
2023-05-03 9:41 ` Richard Henderson [this message]
2023-05-03 16:31 ` Stafford Horne
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