From owner-sc22wg14+sc22wg14-domo2=www.open-std.org@open-std.org Wed Mar 11 23:14:04 2026 Return-Path: X-Original-To: sc22wg14-domo2 Delivered-To: sc22wg14-domo2@www.open-std.org Received: by www.open-std.org (Postfix, from userid 521) id 0D2F5356D61; Wed, 11 Mar 2026 23:14:03 +0100 (CET) Delivered-To: sc22wg14@open-std.org Received: from mail-dy1-f174.google.com (mail-dy1-f174.google.com [74.125.82.174]) by www.open-std.org (Postfix) with ESMTP id 6CDB3356AA9 for ; Wed, 11 Mar 2026 23:14:02 +0100 (CET) Received: by mail-dy1-f174.google.com with SMTP id 5a478bee46e88-2b4520f6b32so704014eec.0 for ; Wed, 11 Mar 2026 15:14:02 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1773267241; cv=none; d=google.com; s=arc-20240605; b=ZAkRBvZpbyQCGKVMR/G3+I2rab2nfPoOWSLLGkNY6JzrEBaolJZsvISTd5c5uMpVj5 /VHgt37v5WXYEuA3GT2Z6CGw3RFWLRahz3Tr60WaYWaMbZjZ+B+mzIMEBXU27fG9Cjd8 bw36eoio/DS+X2z6oq1y5Z1mxzpdDSXqvw4vvHeKiAt9hSp6rOpvrQcqndrLr7lcwMWD gbYJcPaYPZF7aoB4M0QVKe7ZqU1DBPfoxeZmpciv3RgpfTV0bDW/SwcIazXYntYgUE3n /p1yI9Pja3Hr/rNtdpt9EEEjoWWyITcx/rl6HY5udlkdSmPm9wwS0NwlglJV9c1jc+s9 AXAg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605; h=to:subject:message-id:date:from:mime-version:dkim-signature; bh=rYTB716WqqCcJ1BcxWckN4ACXl9lepR6e1cwPH6cn9E=; fh=ArEjJguew1GBOj/hflxzJsqbN9INf8uHQLf+eHp70sw=; b=iKnCCJQbtFxKZKSI/AdfwZbj/96zGSHY1acn3aQJ8IrTDb/ulPCLSBSbUTpCkBKsd3 NEhr5v5ToyPaVL/w2XrISthIbVMhxwhsokgHO//LpIAmLprqf7h6EEn52XVFmwLxYbog h9pnjftjUF1pgdE6c87IO/WvxEf7nbiiZJJn1IM1PsUNSj3MBwkCAdpJGZiKVDtRCoAZ kv0iUBlRhH3eW9Ji9RCLBGxUZKo7FL82u2jQ8fppFkODd5U4D4O0Fh+/TN0JKUC4yDcD jReLgbiZDAWfOYe2PP73u2yA3uUptOqxyQHjxgQN3aDkPt1a1sGqG7t1VYqiQ35RFCpT oD5Q==; darn=open-std.org ARC-Authentication-Results: i=1; mx.google.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1773267241; x=1773872041; darn=open-std.org; h=to:subject:message-id:date:from:mime-version:from:to:cc:subject :date:message-id:reply-to; bh=rYTB716WqqCcJ1BcxWckN4ACXl9lepR6e1cwPH6cn9E=; b=B80BvlwLpOLNxuuprbKr0stWdqFZRNWDRbfuju94CpVkoH2lL7YhtPC+OC91eYcxu6 GMUOA9K983ez+C2sA2jmTu8V0e4XNucKpxePiOfAz3AaMMEtBOpDVeV0TO8j896Rzlp1 3zf1mhFGfHeXqRYGfK/5REn9wykSI9ODsvb4hEL5D0g32FlhqJU3KwVNs8Q5ILO+SINu E295jynhva6bpvhZAQqsTrZJZ5jx0Y/3v5JQx5CRg4AiUTZcAsk3Z9qcW+GIWCU+25YH qfQZII/HK6SHCWYsIktk1Fp7iurQL0u6bNsytMic+W6XU1ZEYtdtdCdzd5lJ4W+I5ZSC QHzQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1773267241; x=1773872041; h=to:subject:message-id:date:from:mime-version:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rYTB716WqqCcJ1BcxWckN4ACXl9lepR6e1cwPH6cn9E=; b=nDgyVmVDngGNHOaYJLxXB3r+A2FvAMo4XmaQFhZvPSVp2u/Gv+LOHhHw+NVV6d59F1 Kf5yqkN9/OpzfnalqtGU3jlVbXki9/yH/DyyQsgnlGKFHb3pX2bKco0dJyvGidjMa+qG R3/0DRwQ8A+O2nvGJlqjum7/M4OBAA6/fhjRnObfmd9EppHfV1mRbx/P0F5FwdreTHln 4nq72kpxZczDoQ4vIDs4ZNOTu7f+kvloXqB2kJNjWsCX65DdRYuvZJqoo4xrYjsrQhES 8meLatyFuCH5I4EMqJ+wOK0PjKnRVVHYL/rOXToeIznp9nUP1b81HxZOEC1zhlP0oSf+ xykw== X-Gm-Message-State: AOJu0Yz5t9PN5pKsFIsReMdsqnsp5ARwFIuqvnsg9CvssW+nyh39QEEq Au2ZEJXiiQuYHYR+MDOldy+E+XwW5ovhZYaEcEyTWzyqi9l2mxlCUBMIUP3gLRHaQj6NgBxe0KU yQZrU/AThj9o8B04Hi35dbIY4GgvOhTnW+p02 X-Gm-Gg: ATEYQzxa2IS2dayB183J1GUI4K91Zg64TBJXBvGX5HEEr1JY8jrAVve6SXmlbVi13tr U7MevsOkV7wpnsFwuv84v6q6qgQxVpDdr/X5hlLHu/WAwh5qxbjcozYetM9FuQ5uM4wAz1Czhi6 cjprHcJfKCEElltKWX8TtCL0nfLfsyH2i4FVgupkcDkwVTslDM/cJYpYIOAwQTURAsFYlkfG4UJ mgQ+aXRFTMLgTzX2xE3eRw7QUjktQLYfcT07X7bPqDt4WFkp2BMCfM8sVYqQcCJRH0FTaBlrhVm 6xT4BjP5EynTGOSLm3RL96fv2I4om7j2tprISQM3qA3DZOGPl4AA9lrmQ0IzZ+2Y3g== X-Received: by 2002:a05:693c:2b0c:b0:2ba:a465:3a20 with SMTP id 5a478bee46e88-2be8a2e2edcmr1657885eec.24.1773267241010; Wed, 11 Mar 2026 15:14:01 -0700 (PDT) MIME-Version: 1.0 From: Christopher Bazley Date: Wed, 11 Mar 2026 22:13:48 +0000 X-Gm-Features: AaiRm50GRjsoOd0vr1DgiGfs7jMNUdMRuD5ZUUMVZxw4-P8wOYklfFvtBXPeTr0 Message-ID: Subject: N3762 Add type-safe minimum and maximum type-generic macros To: wg14 Content-Type: text/plain; charset="UTF-8" Sender: owner-sc22wg14@open-std.org Precedence: bulk Dear all, I have created the following test program to investigate how the behaviour of the stdc_min macro proposed by N3762 differs from two other implementations: - a classic-style simple macro definition similar to that given in The C Programming Language (1988, K&R). - a simple implementation of the same thing using C11 _Generic to avoid multiple evaluation. I took the implementation of stdc_min from https://gustedt.gitlabpages.inria.fr/ellipsis/ellipsis-minmax_8h_source.xhtml#l00155 because I believe it is intended to have the same behaviour. Some things I consider noteworthy: - stdc_min often produces a different answer from the macros whose usage it is most likely to be used to replace. - Even when stdc_min produces the same answer as the two simpler macro definitions, it often produces a different type. I think most programmers would be quite surprised by the fact that the type of _STDC_min(1u,1) is 'int' rather than 'unsigned int'. - Unlike C's usual arithmetic conversion rules, stdc_min does not have platform-dependent behaviour. (Compare the results of KRMIN(1l,1u) for MinGW gcc 15.2.0 and ARM64 GCC trunk, for example.) If you consider existing practice deficient then presumably none of this is concerning. I think providing macros that do something different from most existing implementations of the same functionality is a bit risky, even if the behaviour of these new macros is arguably better designed. It prevents the standard macros being used as a drop-in replacement. I'd rather leave the diagnosis of mixed-signedness arithmetic to the compiler, which seems to be what the designer of _Generic intended. https://godbolt.org/z/vx53bjYjG #include #define DEF_MIN(N, T) \ static T N ## min(T x, T y) { return x < y ? x : y; } DEF_MIN(ll, long long) DEF_MIN(l, long) DEF_MIN(i, int) DEF_MIN(u, unsigned) DEF_MIN(ul, unsigned long) DEF_MIN(ull, unsigned long long) // My macro, created for this demo #define CBMIN(X, Y) \ _Generic((X) + (Y), \ long long: llmin((X), (Y)), \ long: lmin((X), (Y)), \ int: imin((X), (Y)), \ unsigned: umin((X), (Y)), \ unsigned long: ulmin((X), (Y)), \ unsigned long long: ullmin((X), (Y))) // Check if promoted X has a signed type. #define _STDC_signed_mm(X) \ ((typeof(+(X)))-1 < 0) // From https://gustedt.gitlabpages.inria.fr/ellipsis/ellipsis-minmax_8h_source.xhtml#l00155 #define _STDC_mintype(X, Y) \ _Generic((char(*)[1 /* never zero */ \ | (_STDC_signed_mm(X)<<1) \ | (_STDC_signed_mm(Y)<<2) \ | (_STDC_signed_mm((X)+(Y))<<3)] \ )nullptr, \ char(*)[3]: +(X), \ char(*)[5]: (typeof(+(Y)))(X), \ default: (typeof((X)+(Y)))(X)) // X converted to the type for the max feature. #define _STDC_maxtype(X, Y) ((typeof((X)+(Y)))(X)) #define _STDC_min(X, Y) \ (((((X) < 0) != ((Y) < 0)) \ ? ((X) < 0) \ : (_STDC_maxtype(X, Y) < _STDC_maxtype(Y, X))) \ ? _STDC_mintype(X, Y) \ : _STDC_mintype(Y, X)) // Classic-style macro #define KRMIN(A, B) ((A) < (B) ? (A) : (B)) #define PTYPE(T) \ _Generic((T), \ long long: "long long", \ long: "long", \ int: "int", \ unsigned: "unsigned", \ unsigned long: "unsigned long", \ unsigned long long: "unsigned long long") #define TEST(A, B) printf("KRMIN("#A "," #B ") = 0x%llx, type is %s.\n" \ "CBMIN("#A "," #B ") = 0x%llx, type is %s.\n" \ "_STDC_min("#A "," #B ") = 0x%llx, type is %s.\n\n", \ (unsigned long long)KRMIN(A, B), PTYPE(KRMIN(A, B)), \ (unsigned long long)CBMIN(A, B), PTYPE(CBMIN(A, B)), \ (unsigned long long)_STDC_min(A, B), PTYPE(_STDC_min(A, B))) int main(void) { // n3762: Otherwise, minType is the same as maxType. /* C2Y: Otherwise, if both operands have signed integer types or both have unsigned integer types, the operand with the type of lesser integer conversion rank is converted to the type of the operand with greater rank. */ TEST(1, 2); // int TEST(2, 1); // int TEST(-2, -1); // int TEST(-1, -2); // int TEST(1, -1l); // long TEST(1, -1ll); // long long TEST(1, 1l); // long TEST(1, 1ll); // long long TEST((unsigned short)1, -1); // int TEST((unsigned char)1, -1); // int TEST(-1, (unsigned short)1); // int TEST(-1, (unsigned char)1); // int TEST(1u, 1ul); // unsigned long TEST(1u, 1ull); // unsigned long long // n3762: If one of the types A or B is signed and the other is unsigned, minType is the signed type. /* C2Y: Otherwise, if the operand that has unsigned integer type has rank greater or equal to the rank of the type of the other operand, then the operand with signed integer type is converted to the type of the operand with unsigned integer type. */ TEST(1u, 1); // unsigned or int ****** DIFFERENT FROM C ****** TEST(1, 1u); // unsigned or int ****** DIFFERENT FROM C ****** TEST(1u, 2); // unsigned or int ****** DIFFERENT FROM C ****** TEST(2, 1u); // unsigned or int ****** DIFFERENT FROM C ****** TEST(1u, -1); // unsigned or int ****** DIFFERENT FROM C ****** TEST(1ul, -1); // unsigned long or int ****** DIFFERENT FROM C ****** TEST(1ull, -1); // unsigned long long or int ****** DIFFERENT FROM C ****** TEST(-1, 1u); // unsigned or int ****** DIFFERENT FROM C ****** TEST(-1, 1ul); // unsigned long or int ****** DIFFERENT FROM C ****** TEST(-1, 1ull); // unsigned long long or int ****** DIFFERENT FROM C ****** /* C2Y: Otherwise, if the type of the operand with signed integer type can represent all the values of the type of the operand with unsigned integer type, then the operand with unsigned integer type is converted to the type of the operand with signed integer type. (THIS RULE IS PLATFORM DEPENDENT.) */ TEST(1l, 1u); // long or unsigned long ****** DIFFERENT FROM C ****** TEST(1ll, 1u); // long long /* C2Y: Otherwise, both operands are converted to the unsigned integer type corresponding to the type of the operand with signed integer type. (THIS RULE IS PLATFORM DEPENDENT.) */ TEST(1ll, 1ul); // unsigned long long or long long ****** DIFFERENT FROM C ****** return 0; } Christopher