From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_REPLYTO_END_DIGIT, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id C45261F4B4 for ; Sun, 11 Oct 2020 16:44:13 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id ABF6338618A8; Sun, 11 Oct 2020 16:43:55 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org ABF6338618A8 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1602434635; bh=yzAgWgF9mhKy/kKX/y0fHZo8Q5uJhEcMBBl1raABagk=; h=Subject:To:References:Date:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=Qtzgy9GswFCuW0WV2T86uRhHmds/r0vNNMrGK1R0ESD5idJZtLnLDgqntDTlM+m4i a25C4TlEyio9wQzoVqOxSEaTGUDqc91iM41OilrzmSkBGPhtm/qspZONk5Yn/EweKk KJepaQhGcClFQlFP8nbjIB0bmXPjRNBJH3bWqiHw= 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 427A9385ED4D for ; Sun, 11 Oct 2020 16:43:50 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 427A9385ED4D Received: by mail-wm1-x344.google.com with SMTP id k18so15011896wmj.5 for ; Sun, 11 Oct 2020 09:43:50 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=yzAgWgF9mhKy/kKX/y0fHZo8Q5uJhEcMBBl1raABagk=; b=f5LhKfekkBtHzfLy/Vx/D6+IdO2DbloSH2iKo+/6/E+st3V3zv9XCTwKQvqqdp+2wW f0qYH6kvCMfPTkwHSj+86zJexF8tNXy6BzElxGGCKRS3PG43t3Ai1o5cgvVDaeSFLQST dff+k8oKGf3IO7Y64idkOrFJnN61yWOOg4IGLAPxf4C4JlzHlHCftmKJSms8ZMGj7v2+ 0nbdrXFCxuUT2BMEJTPqDZjoYP8W0VO02h3ihqefcE8KavP9gPmnaVr3rCi1HR6yZRuv mz84uP6Dojzmdh3v1GHftP2Yqw1ChrCrecmhA/V3dviC3PbT5GNLEhPCVhsYeEnIyGiC zoQg== X-Gm-Message-State: AOAM5312eUqrYsu/dAaBJlIbQDrAfse++WA9nkelKZRfiAcjjJ0GbrVG +PoBleybGt9a/XfgiS9DD8Uqm/+hEZY= X-Google-Smtp-Source: ABdhPJwMlUbeD2gRfxPdD32kFrNM5R3CniGrqAwCxx//4ML9IX0CVXg5RyUNHxugPq+5LdRQB131VA== X-Received: by 2002:a1c:6788:: with SMTP id b130mr7733457wmc.91.1602434629239; Sun, 11 Oct 2020 09:43:49 -0700 (PDT) Received: from [192.168.1.143] ([170.253.60.68]) by smtp.gmail.com with ESMTPSA id c8sm22597111wmd.18.2020.10.11.09.43.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 11 Oct 2020 09:43:48 -0700 (PDT) Subject: Ping: Re: [PATCH v4] : Add nitems() To: libc-alpha@sourceware.org References: <20200928191237.32063-1-colomar.6.4.3@gmail.com> Message-ID: Date: Sun, 11 Oct 2020 18:43:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200928191237.32063-1-colomar.6.4.3@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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: , From: Alejandro Colomar via Libc-alpha Reply-To: Alejandro Colomar Cc: fweimer@redhat.com, gcc@gcc.gnu.org, ville.voutilainen@gmail.com, linux-man@vger.kernel.org, rusty@rustcorp.com.au, 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" Ping. On 2020-09-28 21:12, Alejandro Colomar wrote: > '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. > > __nitems(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 > --- > > A few changes since v3: > > - Macros don't need reserved names in their parameters, > so I simplified those names. > > - I fixed some wrong indentation levels. > > - Renamed __array_len() to __nitems() for consistency. > > > misc/sys/param.h | 47 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 47 insertions(+) > > diff --git a/misc/sys/param.h b/misc/sys/param.h > index d7c319b157..08d4093961 100644 > --- a/misc/sys/param.h > +++ b/misc/sys/param.h > @@ -102,5 +102,52 @@ > #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 __nitems(arr) (sizeof((arr)) / sizeof((arr)[0])) > +# define nitems(arr) (__nitems(arr) + __must_be_array(arr)) > +#endif /* !defined(__cplusplus) */ > + > > #endif /* sys/param.h */ >