From patchwork Tue Sep 22 14:58:45 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alejandro Colomar X-Patchwork-Id: 40474 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id CFDB939878B2; Tue, 22 Sep 2020 15:00:35 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org CFDB939878B2 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1600786835; bh=usg4wSsmo9yfZpzURo8K/L+xg+b2bka9XCSX0nS4/tU=; h=To:Subject:Date:In-Reply-To:References:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=ucEQ1O3hszs1HtnWWSGgHKu3g2MnpLJnSrGoHOJ48gO4LVBOToE+6fEy4KBC+Br5P IDT4CGjMR+wB12ztTHdumIi2oj7JC18jr/hHmM2gM6LLybyqUUqI1og/vRU2Idxgxl g5TgWSL5zBTlpO12W/e5vT/NEus6UPfEGOla1VHk= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by sourceware.org (Postfix) with ESMTPS id 3624139960DC for ; Tue, 22 Sep 2020 15:00:32 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 3624139960DC Received: by mail-wm1-x344.google.com with SMTP id b79so3662400wmb.4 for ; Tue, 22 Sep 2020 08:00:32 -0700 (PDT) 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=usg4wSsmo9yfZpzURo8K/L+xg+b2bka9XCSX0nS4/tU=; b=PN/Qv0deqSS3sKHy0Y6LAzcVIAmYAYO3hJOD4pgd0MQ4Alirr7PVUsA9nSOwD2NNrE kLNsVdI1u1eRRdQW2e/LmevrTYt3onWqg0DG/UeNTauSNB7E6ouyH56DIaTRBS5JyXf1 o0VMbe7iNKZ9k/1aOWnc6WKvlM2Dmjzdn38rpZIWRFHYFlGU9Kp7fGNM6duiQ6ceFAfV R/1cOmPwoVyznGGA2gnEJq0CHYm9+kPZkrSypZH2c1/o2nc5GD7zNQZIyCGFuJjxfBab /bz9OtYYa/N5lNIOjYR7n7AKnkt2CZ9f+O/v1N4Xin+EARhBamT1Rnr1Jboo6xB89pSn PKNg== X-Gm-Message-State: AOAM531j9HVMwndqAFVHziFWG+bekC+KIeI7H7VrEjJ1mpsV8kdppfhn lsOab0wAWNtKtBLBvVqnMba0nWqlXsryKA== X-Google-Smtp-Source: ABdhPJxVA6X9UxTMq9O+yob9ZOu3MDVkPMFmqwM4hwUs1DRHl+gXnTGn1T4sL5QqskI+Y7mjJ32lnQ== X-Received: by 2002:a05:600c:1293:: with SMTP id t19mr1550063wmd.34.1600786830529; Tue, 22 Sep 2020 08:00:30 -0700 (PDT) Received: from localhost.localdomain ([170.253.60.68]) by smtp.googlemail.com with ESMTPSA id y6sm27215861wrn.41.2020.09.22.08.00.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2020 08:00:29 -0700 (PDT) To: libc-alpha@sourceware.org Subject: [RFC] : Add nitems() and snitems() macros Date: Tue, 22 Sep 2020 16:58:45 +0200 Message-Id: <20200922145844.31867-1-colomar.6.4.3@gmail.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <87zh5ixcn9.fsf@oldenburg2.str.redhat.com> References: <87zh5ixcn9.fsf@oldenburg2.str.redhat.com> MIME-Version: 1.0 X-Spam-Status: No, score=-9.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=unavailable autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Alejandro Colomar via Libc-alpha From: Alejandro Colomar Reply-To: Alejandro Colomar Cc: fweimer@redhat.com, gcc@gcc.gnu.org, ville.voutilainen@gmail.com, linux-man@vger.kernel.org, Alejandro Colomar , linux-kernel@vger.kernel.org, libstdc++@gcc.gnu.org, libc-coord@lists.openwall.com, jwakely@redhat.com, enh@google.com Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" '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 'snitems()' is equivalent to nitems(), but it returns a 'ptrdiff_t' instead of a 'size_t'. It is useful for comparison with signed integer values. 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 --- [[ CC += linux-man ]] A few more things: I copied the contents of this patch into my system and recompiled my projects to use these definitions, and they worked correctly. A few more notes: For linux-man (which is CC'd): When/if this patch is accepted, I'll write nitems.3 (and snitems.3). For LKML (which is CC'd): Please comment if there are any conflicts with your macro '__must_be_array()' (or any other conflicts, BTW). Cheers, Alex misc/sys/param.h | 57 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/misc/sys/param.h b/misc/sys/param.h index d7c319b157..f11f5dd4fd 100644 --- a/misc/sys/param.h +++ b/misc/sys/param.h @@ -102,5 +102,62 @@ #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; + } + +template + constexpr inline std::ptrdiff_t + snitems(const _Tp(&)[_Len]) __THROW + { + return _Len; + } +# else /* __cplusplus < 201103L */ +template + char (&__nitems_chararr(const _Tp(&)[_Len]))[_Len]; + +# define nitems(_Arr) (sizeof(__nitems_chararr(_Arr))) +# define snitems(_Arr) (static_cast(nitems(_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)) +# define snitems(_Arr) ((ptrdiff_t)nitems(_Arr)) +#endif /* !defined(__cplusplus) */ + #endif /* sys/param.h */