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Mon, 22 Jun 2020 17:33:20 -0700 (PDT) Subject: Re: [PATCH v2] target/i386: reimplement fpatan using floatx80 operations To: Joseph Myers , qemu-devel@nongnu.org, rth@twiddle.net, ehabkost@redhat.com References: From: Paolo Bonzini Message-ID: <27588539-95cc-f10f-b8c2-c263b56c921a@redhat.com> Date: Tue, 23 Jun 2020 02:33:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=pbonzini@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/22 02:57:26 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 23/06/20 02:01, Joseph Myers wrote: > The x87 fpatan emulation is currently based around conversion to > double. This is inherently unsuitable for a good emulation of any > floatx80 operation. Reimplement using the soft-float operations, as > for other such instructions. > > Signed-off-by: Joseph Myers Queued, thanks. Just one question: do recent processors still use the same CORDIC approximations as the 8087, and if so would it be better or simpler to do that instead of using a good implementation such as this one? Thanks, Paolo