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[174.21.143.238]) by smtp.gmail.com with ESMTPSA id j19sm5220171pjy.40.2020.06.26.08.58.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Jun 2020 08:58:19 -0700 (PDT) Subject: Re: fpu/softfloat: a question on BFloat 16 support on QEMU To: LIU Zhiwei , =?UTF-8?Q?Alex_Benn=c3=a9e?= References: <87img15zfv.fsf@linaro.org> <29d37daf-ced3-8555-7d25-00baacbb4449@c-sky.com> From: Richard Henderson Message-ID: <9a12aa2e-ee66-ffb5-8598-775615e6ba24@linaro.org> Date: Fri, 26 Jun 2020 08:58:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <29d37daf-ced3-8555-7d25-00baacbb4449@c-sky.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::634; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x634.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "qemu-devel@nongnu.org Developers" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/17/20 12:09 AM, LIU Zhiwei wrote: > If I want to test bfloat16 interfaces, could you give some advice? Should I > need to modify berkeley-testfloat-3 to support the bfloat16 test. I think we'll have to write some new code for this. Easiest might be: (1) shift left to convert bfloat16 to float32, (2) if the current rounding mode is directed (float_round_{down,up,to_zero}), use that; otherwise use float_round_to_odd so that we can get the correct bfloat16 rounding later. (3) use the float32 arithmetic routine. (4) round to bfloat16 as per the current mode. This should not require too much new code. r~