From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F223CC4727E for ; Fri, 25 Sep 2020 20:33:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B65CE20838 for ; Fri, 25 Sep 2020 20:33:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CgaQei8l" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729058AbgIYUde (ORCPT ); Fri, 25 Sep 2020 16:33:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52368 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727067AbgIYUXf (ORCPT ); Fri, 25 Sep 2020 16:23:35 -0400 Received: from mail-wm1-x341.google.com (mail-wm1-x341.google.com [IPv6:2a00:1450:4864:20::341]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25556C0613AE; Fri, 25 Sep 2020 12:38:14 -0700 (PDT) Received: by mail-wm1-x341.google.com with SMTP id v12so185629wmh.3; Fri, 25 Sep 2020 12:38:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=jbsgOVHvmUXSEBjLnfyZSNTlMb8phG4kk/fXxKZ+eRg=; b=CgaQei8lRddJ8NgvJLf0DNXjKCz/qNN2jDqyE8o0kPqx8+kXKWgG4p5cW4igqBWvH+ d8V2y0Urtt5A4NqnNJ84knmZAdEnK//UE/VE1IOpzm4AXV69Yvi8h1nBwAtQGmwzgAvo jdbDxIgRDppT2IjpP2UL9L3Hg1Ni5O4THmuyVbDZqhzvsDXQhobCSzSQtykYJqKGXEYg 7H1I02idgebVDnI7tQF3JMEHWrXUH3y0BOJWByEHOehEAfbr9MJsLhMmWvEtVwGmrMi4 B3P8Sw2mEjDLog0IZN821nreyuN24M/5HorDeFwHwQlG41zTjbP6rOgYes/aBk88eGh9 9ABg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=jbsgOVHvmUXSEBjLnfyZSNTlMb8phG4kk/fXxKZ+eRg=; b=IglwbCMqaVCuSymij1ja5ycTuzFQ/011GdYO67NItKpOgwoKiPdRqLyYu6iu7JhQ9l 9jJ6eZZAZI4LfICyQdi0Rs7H0BTaHhsVDXoUVZIv0HcoCfCBiJuozYzAgr2kd9eXhfQW lrXeLXdDy4BBoxs+L8rpwelDWuBeZhF4FMHWo9HYm68b3Mh6yGACVQqPKBvCe5Iw+9iu ljWLl1xBdKpRthCNhNGU0V+mmu2+lD2bXPJdXthTKJI8Mq9m5mZNpDOz3n5dZyJKwlVX 16mOmWon5P2qk1maU3qIlNBei6fPlPK6A6oMZEBONNkudInNymGcro5Ze8LBNPnvlkut R1TA== X-Gm-Message-State: AOAM533a9eAmVTk0IzpG1fJqdlN+64J81TwKt1dW+9cqZmzBzM9YQttO Cbm4nihVusjZ3YUfKv3J6d4= X-Google-Smtp-Source: ABdhPJyqlDntoAWN5Ogrw2rGYEXT5bafB540fMrgyreKkEcl6WZOTJklZWUGNDReomLwbqLRszc1eA== X-Received: by 2002:a1c:e389:: with SMTP id a131mr117683wmh.181.1601062692684; Fri, 25 Sep 2020 12:38:12 -0700 (PDT) Received: from localhost.localdomain ([93.115.133.118]) by smtp.googlemail.com with ESMTPSA id m18sm50368wmg.32.2020.09.25.12.38.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Sep 2020 12:38:12 -0700 (PDT) From: Alejandro Colomar To: libc-alpha@sourceware.org Cc: libc-coord@lists.openwall.com, libstdc++@gcc.gnu.org, gcc@gcc.gnu.org, linux-kernel@vger.kernel.org, linux-man@vger.kernel.org, jwakely@redhat.com, fweimer@redhat.com, ville.voutilainen@gmail.com, enh@google.com, rusty@rustcorp.com.au, colomar.6.4.3@gmail.com Subject: [PATCH v3] : Add nitems() Date: Fri, 25 Sep 2020 21:37:29 +0200 Message-Id: <20200925193728.30351-1-colomar.6.4.3@gmail.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 'nitems()' calculates the length of an array in number of items. It is safe: if a pointer is passed to the macro (or function, in C++), the compilation is broken due to: - In >= C11: _Static_assert() - In C89, C99: Negative anonymous bitfield - In C++: The template requires an array Some BSDs already provide a macro nitems() in , although it usually doesn't provide safety against pointers. This patch uses the same name for compatibility reasons, and to be the least disruptive with existing code. This patch also adds some other macros, which are required by 'nitems()': __is_same_type(_A, _B): Returns non-zero if the two input arguments are of the same type. __is_array(_Arr): Returns non-zero if the input argument is of an array type. __must_be(_Expr, _Msg): Allows using _Static_assert() everywhere an expression can be used. It evaluates '(int)0' or breaks the compilation. __must_be_array(_Arr): It evaluates to '(int)0' if the argument is of an array type. Else, it breaks compilation. __array_len(_Arr): It implements the basic sizeof division needed to calculate the array length. P.S.: I'd like to put this patch in the public domain. Signed-off-by: Alejandro Colomar --- misc/sys/param.h | 51 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/misc/sys/param.h b/misc/sys/param.h index d7c319b157..d88cbacc9c 100644 --- a/misc/sys/param.h +++ b/misc/sys/param.h @@ -102,5 +102,56 @@ #define MIN(a,b) (((a)<(b))?(a):(b)) #define MAX(a,b) (((a)>(b))?(a):(b)) +/* Macros related to the types of variables */ +# define __is_same_type(_A, _B) __builtin_types_compatible_p(__typeof__(_A), \ + __typeof__(_B)) +# define __is_array(_Arr) (!__is_same_type((_Arr), &(_Arr)[0])) + +/* Macros for embedding _Static_assert() in expressions */ +# if __STDC_VERSION__ >= 201112L +# define __must_be(_Expr, _Msg) ( \ + 0 * (int)sizeof( \ + struct { \ + _Static_assert((_Expr), _Msg); \ + char _ISO_C_forbids_a_struct_with_no_members; \ + } \ + ) \ +) +# else +# define __must_be(_Expr, _Msg) ( \ + 0 * (int)sizeof( \ + struct { \ + int : (-!(_Expr)); \ + char _ISO_C_forbids_a_struct_with_no_members; \ + } \ + ) \ +) +# endif + +# define __must_be_array(_Arr) __must_be(__is_array(_Arr), "Must be an array!") + +/* Macros for array sizes */ +#if defined(__cplusplus) +# if __cplusplus >= 201103L +template + constexpr inline std::size_t + nitems(const _Tp(&)[_Len]) __THROW + { + return _Len; + } + +# else /* __cplusplus < 201103L */ +template + char + (&__nitems_chararr(const _Tp(&)[_Len]))[_Len]; + +# define nitems(_Arr) (sizeof(__nitems_chararr(_Arr))) +# endif /* __cplusplus < 201103L */ + +#else /* !defined(__cplusplus) */ +# define __array_len(_Arr) (sizeof(_Arr) / sizeof((_Arr)[0])) +# define nitems(_Arr) (__array_len(_Arr) + __must_be_array(_Arr)) +#endif /* !defined(__cplusplus) */ + #endif /* sys/param.h */ -- 2.28.0