From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-x444.google.com (mail-wr1-x444.google.com [IPv6:2a00:1450:4864:20::444]) by sourceware.org (Postfix) with ESMTPS id 0A8A13858D37 for ; Tue, 27 Oct 2020 11:38:28 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 0A8A13858D37 Received: by mail-wr1-x444.google.com with SMTP id n6so1467084wrm.13 for ; Tue, 27 Oct 2020 04:38:27 -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=t8iT8vBhgGfFcPExE13uV2njX3ArLHEUaSwDhfxlKNY=; b=C3arZC441iZRk7Ab8uL9N5OENMrM2gdFHKj3XJs+LMfzjF1zawX1KIRJXp+3aBP/yd ZqT6Lgx32Oj47PVobQNqRd9oXChRTrAIAtCimW00Hhq/LvUksL27RWd76WPwLkrWaywA uNdqqbDDwpUglRQ2sVf7xVTtc+1UwpYav9CotOZRjs8T+LUVjTyfqH6R/dwVOZJyyFlJ B6cbHL+3JyhFSOZrQWXU/CbWKtU1Pegwzomky5SqeEL6ZdDgrbefm7qfEYtfmUiwq2L8 ba4/7+8Ai8AgzmRkvi21I4R/NHlKdgAgXfVe4jC0BDXFarbqYYtNi0AIyeshUkUDNETc Rh8A== X-Gm-Message-State: AOAM533GYG/JlVgEp7nyX5P8F2uZARb4U6j05r5yRhl0zzfHpduSJQpq /YLzIqk3LGcgXeiexeJ/Cqg= X-Google-Smtp-Source: ABdhPJzzdrvXV7uYHSg4jpIFgiX0/oVNeTVHOqapl7/VC1z0Ahywpjhh5pmu0K3CsNRokdo1Pg+yTQ== X-Received: by 2002:a5d:468f:: with SMTP id u15mr2403894wrq.154.1603798707103; Tue, 27 Oct 2020 04:38:27 -0700 (PDT) Received: from [192.168.1.143] ([170.253.60.68]) by smtp.gmail.com with ESMTPSA id b5sm1616273wrs.97.2020.10.27.04.38.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2020 04:38:26 -0700 (PDT) Subject: Ping(2): [PATCH v4] : Add nitems() To: libc-alpha@sourceware.org, libc-coord@lists.openwall.com Cc: 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 References: <20200928191237.32063-1-colomar.6.4.3@gmail.com> From: Alejandro Colomar Message-ID: <2bbe4b2f-46c1-4caa-fbd9-6c8efbc0c7e5@gmail.com> Date: Tue, 27 Oct 2020 12:38:25 +0100 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-Spam-Status: No, score=-11.7 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=ham 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-List-Received-Date: Tue, 27 Oct 2020 11:38:29 -0000 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 */ >