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[174.21.149.226]) by smtp.gmail.com with ESMTPSA id p8sm6797085pjd.10.2020.04.17.16.58.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Apr 2020 16:58:35 -0700 (PDT) Subject: Re: [PATCH 2/4] target/arm: Implement SVE2 RADDHNB, RADDHNT From: Richard Henderson To: Stephen Long , qemu-devel@nongnu.org References: <20200417162231.10374-1-steplong@quicinc.com> <20200417162231.10374-3-steplong@quicinc.com> <7593864c-828f-5c03-c3d5-8ba8eab8cd6a@linaro.org> Message-ID: Date: Fri, 17 Apr 2020 16:58:33 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <7593864c-828f-5c03-c3d5-8ba8eab8cd6a@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::1043 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-arm@nongnu.org, apazos@quicinc.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/17/20 2:24 PM, Richard Henderson wrote: > On 4/17/20 9:22 AM, Stephen Long wrote: >> +#define DO_RADDHN(N, M, SH) ((N + M + (1 << (SH - 1))) >> SH) > > This formula will overflow. See DO_RSHR -- with some added parenthesis, we > could actually reuse that macro. My bad. While it does overflow, all of these operations are truncating not saturating, and moreover truncate to halfesize bits. Therefore overflow doesn't matter. r~