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[2.142.216.190]) by smtp.gmail.com with ESMTPSA id 19sm398374wmo.39.2021.09.03.14.09.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Sep 2021 14:09:25 -0700 (PDT) Subject: Re: [PATCH v2 04/19] host-utils: add 128-bit quotient support to divu128/divs128 To: Luis Fernando Fujita Pires , "qemu-devel@nongnu.org" , "qemu-ppc@nongnu.org" References: <20210831164007.297781-1-luis.pires@eldorado.org.br> <20210831164007.297781-5-luis.pires@eldorado.org.br> From: Richard Henderson Message-ID: <3bcc33e9-7076-e3ba-df86-1950cd1caa36@linaro.org> Date: Fri, 3 Sep 2021 23:09:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::436; envelope-from=richard.henderson@linaro.org; helo=mail-wr1-x436.google.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 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=-0.888, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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: "groug@kaod.org" , "david@gibson.dropbear.id.au" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/2/21 11:07 PM, Luis Fernando Fujita Pires wrote: > From: Richard Henderson >> Hmm. I'll note that we have a better divmod primitive in tree, but we aren't >> using it >> here: udiv_qrnnd in include/fpu/softfloat-macros.h. > > Good to know! I'll change to a (much simpler) implementation using udiv_qrnnd. > Any pointers on what would be a good place to put udiv_qrnnd, so it can be used by softloat.c and host-utils.c? Would host-utils.h be ok? Yeah, that should be fine. Note that udiv_qrnnd requires that the divisor be normalization, i.e. the msb of the denominator must be set. So: int sh = clz64(den); uint64_t q, r; q = udiv_qrnnd(&r, num_hi, num_lo, den << sh); q <<= sh; r >>= sh; IIRC. You'll probably want to have a look at gmp source, from which this comes for best practice in implementing a larger division. r~