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([2602:ae:1541:f901:8bb4:5a9d:7ab7:b4b8]) by smtp.gmail.com with ESMTPSA id s11-20020a170902988b00b001991f3d85acsm3107007plp.299.2023.04.07.09.46.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 07 Apr 2023 09:46:02 -0700 (PDT) Message-ID: <962561ec-f3e1-0c25-67e0-1130f1f3e63f@linaro.org> Date: Fri, 7 Apr 2023 09:46:00 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [RFC PATCH v2 30/44] target/loongarch: Implement vclo vclz Content-Language: en-US To: gaosong , qemu-devel@nongnu.org References: <20230328030631.3117129-1-gaosong@loongson.cn> <20230328030631.3117129-31-gaosong@loongson.cn> From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::102a; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x102a.google.com X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 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=-2.03, 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: 2.1.29 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 4/7/23 00:40, gaosong wrote: > > 在 2023/4/2 上午11:34, Richard Henderson 写道: >> On 3/27/23 20:06, Song Gao wrote: >>> +#define DO_CLO_B(N)  (clz32((uint8_t)~N) - 24) >>> +#define DO_CLO_H(N)  (clz32((uint16_t)~N) - 16) >> >> I think this is wrong. > It is wried,  the result is always right. :-\ > and  (clz32(~N) - 24)  or (clz32((uint32_t)~N) - 24) is wrong. >> You *want* the high bits to be set, so that they are ones, and included in the count, >> which you then subtract off.  You want the "real" count to start after the 24th leading 1. >> > Yes, > and  we use clz32(),   how about the following way? > > #define DO_CLO_B(N)  (clz32( ~N & 0xff) -24) > #define DO_CLO_H(N)  (clz32( ~N & 0xffff) -16) Ah yes, I see. My mistake. Either old or new formulation is fine. Reviewed-by: Richard Henderson r~