From: Jeff Law <jeffreyalaw@gmail.com>
To: 钟居哲 <juzhe.zhong@rivai.ai>, gcc-patches <gcc-patches@gcc.gnu.org>
Cc: "kito.cheng" <kito.cheng@gmail.com>,
"kito.cheng" <kito.cheng@sifive.com>, palmer <palmer@dabbelt.com>,
palmer <palmer@rivosinc.com>, "rdapp.gcc" <rdapp.gcc@gmail.com>
Subject: Re: [PATCH] RISC-V: Add rounding mode operand for floating point instructions
Date: Mon, 15 May 2023 21:56:04 -0600 [thread overview]
Message-ID: <a9d9c01a-e094-6a20-e636-4549b1d50b7b@gmail.com> (raw)
In-Reply-To: <E7993A05483AAA09+202305152154519282643@rivai.ai>
On 5/15/23 07:54, 钟居哲 wrote:
> I don't know why we should not add frm vfsqrt.v since I saw topper (LLVM
> maintainer) said we should
> not add frm into vsqrt.v. Maybe kito knows the reason ?
I'm pretty sure this is referring to the estimator. The documentation
is very clear that the sqrt estimator is independent of the rounding mode.
While it's not as explicit in the RV manual, a real sqrt instruction
must round to be usable in an IEEE compliant way. If it didn't honor
rounding modes we would largely be unable to use the [v]fsqrt instructions.
Jeff
prev parent reply other threads:[~2023-05-16 3:56 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-15 11:49 juzhe.zhong
2023-05-15 13:44 ` Kito Cheng
2023-05-15 13:52 ` Jeff Law
2023-05-15 13:52 ` Jeff Law
2023-05-15 13:54 ` 钟居哲
2023-05-15 14:07 ` Kito Cheng
2023-05-15 14:08 ` 钟居哲
2023-05-15 14:12 ` 钟居哲
2023-05-15 14:22 ` Kito Cheng
2023-05-15 14:24 ` 钟居哲
2023-05-15 14:28 ` 钟居哲
2023-05-15 14:37 ` 钟居哲
2023-05-15 14:41 ` Kito Cheng
2023-05-15 14:55 ` 钟居哲
2023-05-16 3:56 ` Jeff Law [this message]
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