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[209.85.208.51]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a7acab4de47sm403664966b.67.2024.07.28.09.57.20 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 28 Jul 2024 09:57:20 -0700 (PDT) Received: by mail-ed1-f51.google.com with SMTP id 4fb4d7f45d1cf-5af51684d52so2345848a12.1 for ; Sun, 28 Jul 2024 09:57:20 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCVTnVKq1Z2zGL/PePcEpZ+5dWPvZ1LVejOCGaEV4rxxbwQjxbng6Vk1y68xtIJ3uglt5JQIpRBHzfLlPOQCodtdiaE= X-Received: by 2002:a50:a41c:0:b0:5a7:464a:ab9 with SMTP id 4fb4d7f45d1cf-5b020ea8da9mr3235857a12.21.1722185840503; Sun, 28 Jul 2024 09:57:20 -0700 (PDT) MIME-Version: 1.0 References: <402c3c617c29465c898b1af55e3c6095@AcuMS.aculab.com> <74e0b027a908461da879b69b0e12c0de@AcuMS.aculab.com> In-Reply-To: <74e0b027a908461da879b69b0e12c0de@AcuMS.aculab.com> From: Linus Torvalds Date: Sun, 28 Jul 2024 09:57:03 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 4/8] minmax: Simplify signedness check To: David Laight Cc: "linux-kernel@vger.kernel.org" , Jens Axboe , "Matthew Wilcox (Oracle)" , Christoph Hellwig , Andrew Morton , Andy Shevchenko , Dan Carpenter , Arnd Bergmann , "Jason@zx2c4.com" , "pedro.falcato@gmail.com" , Mateusz Guzik , "linux-mm@kvack.org" , Lorenzo Stoakes Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 99E8714001A X-Stat-Signature: 1kwus6n61u9tjgywo7xnkqp67a17erm5 X-Rspam-User: X-HE-Tag: 1722185844-996725 X-HE-Meta: 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 UAHAZT/S +smMvnLqdMCgQG7MDU1tn4xV38xEEIjKFR6rq2JJeXCx/DWHsaPhysXbOSjRQqTixyxgzJHNh7uHJ0OYrhpNKi576G+C6+D1nVUq2SY15BCXha5Hqj7IuuS3ZBWYEjXXtywsfbJmt3wM8QbHAYUNZiz06Wek+mcWsoTtK92rwcIeBqEc7ph6dl6iIDEpzvXRuATc/QHuQSd6kr+DRJtV+I6ZFPpzeVbemrMqT3bXlecfMVYFcXbRsPs0B6dX/zq+N2yXLSYfFRIsLJde3Skjl+ukiwaFLVqIZjdMc4bQZOfn1piT6iLtCkdiFS2J5++Xf3ItrHF6D38ku8dEv8J8tQsoWNuE5hmN4g3zJEbp7Zp2vlskYmOKTc1ScmNRn6tG6B395R6gUbYJdPImziqoIJsSoBm0TMvlgOkMfrJ/Sg+rQLX8yCZIFj4ZYkfMdHVCAxRlrdOuYWvuWTkzBxGKzLNy0fq2w/byWRht5TTPwuivlGJ4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 28 Jul 2024 at 07:21, David Laight wrote: > > +/* Allow if both x and y are valid for either signed or unsigned compares. */ > +#define __types_ok(x, y) \ > + ((__is_ok_signed(x) && __is_ok_signed(y)) || \ > + (__is_ok_unsigned(x) && __is_ok_unsigned(y))) This seems horrendous, exactly because it expands both x and y twice. And the "expand multiple times" was really the fundamental problem. Why not just change the model to say it's a bitmask of "signedness bits", the bits are "signed ok" and "unsigned ok", and turn it into /* Signedness matches? */ #define __types_ok(x, y) \ (__signedness_bits(x) & __signedness_bits(y)) and __signedness_ok() simply does something like "1 if unsigned type, 2 if signed type, 3 if signed positive integer". Something like (very very handwavy, very very untested): __builtin_choose_expr(is_signed_type(typeof(x)), 2+__if_constexpr(x,(x)>0,0), 1) Actually, I think that "__if_constexpr()" could very well be "if known positive value", ie 'x' itself doesn't have to be constant, but "x>0" has to be a constant (the difference being that the compiler may be able to tell that some variable is always positive, even if it's a variable): #define statically_true(x) __builtin_constant_p((x),(x),0) #define is_positive_value(x) statically_true((x)>=0) and then use __builtin_choose_expr(is_signed_type(typeof(x)), 2+is_positive_value(x), 1) and yes, I realize I count zero as a positive value, but writing out "nonnegative()" is annoying and we never care. I guess we could say "is_unsigned_value()"? Linus