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([2607:fb90:80ca:1129:3594:91a:8889:c77a]) by smtp.gmail.com with ESMTPSA id b15sm9929836qtg.82.2021.04.19.08.28.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Apr 2021 08:28:45 -0700 (PDT) Subject: Re: [PATCH] fpu/softfloat: set invalid excp flag for RISC-V muladd instructions To: frank.chang@sifive.com, qemu-devel@nongnu.org, qemu-riscv@nongnu.org References: <20210419055614.28361-1-frank.chang@sifive.com> From: Richard Henderson Message-ID: <448d86ca-28b0-6523-d84b-4f9e867cf01b@linaro.org> Date: Mon, 19 Apr 2021 08:28:40 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210419055614.28361-1-frank.chang@sifive.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::72f; envelope-from=richard.henderson@linaro.org; helo=mail-qk1-x72f.google.com 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no 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: Peter Maydell , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Aurelien Jarno Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/18/21 10:56 PM, frank.chang@sifive.com wrote: > +#elif defined(TARGET_RISCV) > + /* > + * For RISC-V, InvalidOp is set when multiplicands are Inf and zero > + * and returns default NaN. > + */ > + if (infzero) { > + float_raise(float_flag_invalid, status); > + return 3; > + } > + > + if (is_nan(a_cls)) { > + return 0; > + } else if (is_nan(b_cls)) { > + return 1; > + } else { > + return 2; > + } This second half of the function made me go look into the spec to make sure you had got that selection right. But RISCV is always in default_nan mode, so all this is unused (and overridden in pick_nan_muladd). I think for avoidance of confusion, you should use if (infzero) { float_raise(float_flag_invalid, status); } return 3; /* default nan */ r~