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Thu, 28 Nov 2024 06:05:33 -0800 (PST) Received: from [172.20.3.167] ([187.217.227.247]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-29de901327dsm407423fac.15.2024.11.28.06.05.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Nov 2024 06:05:33 -0800 (PST) Message-ID: <034e3bca-5324-414f-bdd7-9572dc98437f@linaro.org> Date: Thu, 28 Nov 2024 08:04:57 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH for-10.0 11/25] target/x86: Set FloatInfZeroNaNRule explicitly To: Peter Maydell , qemu-devel@nongnu.org References: <20241128104310.3452934-1-peter.maydell@linaro.org> <20241128104310.3452934-12-peter.maydell@linaro.org> Content-Language: en-US From: Richard Henderson In-Reply-To: <20241128104310.3452934-12-peter.maydell@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2001:4860:4864:20::2d; envelope-from=richard.henderson@linaro.org; helo=mail-oa1-x2d.google.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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, RCVD_IN_SBL_CSS=3.335, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 11/28/24 04:42, Peter Maydell wrote: > Set the FloatInfZeroNaNRule explicitly for the x86 target. > > Signed-off-by: Peter Maydell > --- > target/i386/tcg/fpu_helper.c | 7 +++++++ > fpu/softfloat-specialize.c.inc | 2 +- > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/target/i386/tcg/fpu_helper.c b/target/i386/tcg/fpu_helper.c > index 53b49bb2977..e9de084a96d 100644 > --- a/target/i386/tcg/fpu_helper.c > +++ b/target/i386/tcg/fpu_helper.c > @@ -173,6 +173,13 @@ void cpu_init_fp_statuses(CPUX86State *env) > */ > set_float_2nan_prop_rule(float_2nan_prop_x87, &env->mmx_status); > set_float_2nan_prop_rule(float_2nan_prop_x87, &env->sse_status); > + /* > + * Only SSE has multiply-add instructions. > + * TODO: this might be wrong, as we never implemented any x86-specific > + * handling for the NaN case for multiply-add. This needs to be checked > + * against the manual. > + */ > + set_float_infzeronan_rule(float_infzeronan_dnan_never, &env->sse_status); This is correct. Section 14.5.2 Fused-Multiply-ADD (FMA) Numeric Behavior has table 14-17 FMA Numeric Behavior. It boils down to selecting the first NaN from A * B + C. Row 3 specifically documents C as the result for A and B both in {0, Finite, Inf}, which includes the infzero case. Reviewed-by: Richard Henderson r~