From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 45B6A3858C3A for ; Sat, 27 Nov 2021 12:00:04 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 45B6A3858C3A Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-364-afgKTllwNdaNn71rkX4ZIw-1; Sat, 27 Nov 2021 07:00:01 -0500 X-MC-Unique: afgKTllwNdaNn71rkX4ZIw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 94FC01030C20; Sat, 27 Nov 2021 12:00:00 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2D2F879450; Sat, 27 Nov 2021 11:59:59 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.16.1/8.16.1) with ESMTPS id 1ARBxvg81761770 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Sat, 27 Nov 2021 12:59:57 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 1ARBxvow1761769; Sat, 27 Nov 2021 12:59:57 +0100 Date: Sat, 27 Nov 2021 12:59:56 +0100 From: Jakub Jelinek To: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org Subject: [PATCH] libstdc++: Implement std::byteswap for C++23 Message-ID: <20211127115956.GV2646553@tucnak> Reply-To: Jakub Jelinek MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-5.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_NUMSUBJECT, KAM_SHORT, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 27 Nov 2021 12:00:14 -0000 Hi! This patch attempts to implement P1272R4 (except for the std::bit_cast changes in there which seem quite unrelated to this and will need to be fixed on the compiler side). While at least for GCC __builtin_bswap{16,32,64,128} should work fine in constant expressions, I wonder about other compilers, so I'm using a fallback implementation for constexpr evaluation always. If you think that is unnecessary, I can drop the __cpp_if_consteval >= 202106L && if !consteval { and } and reformat. The fallback implementation is an attempt to make it work even for integral types that don't have number of bytes divisible by 2 or when __CHAR_BIT__ is e.g. 16. Tested on x86_64-linux, ok for trunk? 2021-11-27 Jakub Jelinek * include/std/bit (__cpp_lib_byteswap, byteswap): Define. * include/std/version (__cpp_lib_byteswap): Define. * testsuite/26_numerics/bit/bit.byteswap/byteswap.cc: New test. * testsuite/26_numerics/bit/bit.byteswap/version.cc: New test. --- libstdc++-v3/include/std/bit.jj 2021-04-13 20:41:50.781976767 +0200 +++ libstdc++-v3/include/std/bit 2021-11-27 12:37:24.399604115 +0100 @@ -78,6 +78,54 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION } #endif +#if __cplusplus > 202002l +#define __cpp_lib_byteswap 202110L + + /// Reverse order of bytes in the object representation of `value`. + template + constexpr enable_if_t::value, _Tp> + byteswap(_Tp __value) noexcept + { +#if __cpp_if_consteval >= 202106L && __CHAR_BIT__ == 8 + if !consteval + { + if constexpr (sizeof(_Tp) == 1) + return __value; + if constexpr (sizeof(_Tp) == 2) + return __builtin_bswap16(__value); + if constexpr (sizeof(_Tp) == 4) + return __builtin_bswap32(__value); + if constexpr (sizeof(_Tp) == 8) + return __builtin_bswap64(__value); + if constexpr (sizeof(_Tp) == 16) +#if __has_builtin(__builtin_bswap128) + return __builtin_bswap128(__value); +#else + return (__builtin_bswap64(__value >> 64) + | (__builtin_bswap64(__value) << 64)); +#endif + } +#endif + + // Fallback implementation that handles even __int24 etc. + using _Up = typename __make_unsigned<__remove_cv_t<_Tp>>::__type; + constexpr _Up __mask = static_cast(~0); + constexpr size_t __bits = __CHAR_BIT__ * sizeof(_Tp); + _Up __val = __value; + for (size_t __i = 0; __i < sizeof(_Tp) / 2; ++__i) + { + size_t __amount1 = __CHAR_BIT__ * __i; + size_t __amount2 = __bits - __amount1 - __CHAR_BIT__; + size_t __diff = __amount2 - __amount1; + _Up __byte1 = __val & (__mask << __amount1); + _Up __byte2 = __val & (__mask << __amount2); + __val = (__val ^ __byte1 ^ __byte2 + ^ (__byte1 << __diff) ^ (__byte2 >> __diff)); + } + return __val; + } +#endif + /// @cond undoc template --- libstdc++-v3/include/std/version.jj 2021-11-17 10:10:08.034949063 +0100 +++ libstdc++-v3/include/std/version 2021-11-27 10:50:44.620238052 +0100 @@ -294,6 +294,7 @@ #if __cplusplus > 202002L // c++2b #define __cpp_lib_adaptor_iterator_pair_constructor 202106L +#define __cpp_lib_byteswap 202110L #define __cpp_lib_invoke_r 202106L #define __cpp_lib_is_scoped_enum 202011L #if __cpp_lib_concepts --- libstdc++-v3/testsuite/26_numerics/bit/bit.byteswap/byteswap.cc.jj 2021-11-27 11:40:50.654149348 +0100 +++ libstdc++-v3/testsuite/26_numerics/bit/bit.byteswap/byteswap.cc 2021-11-27 12:43:00.696889120 +0100 @@ -0,0 +1,112 @@ +// Copyright (C) 2021 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2b" } +// { dg-do compile { target c++23 } } + +#include + +#ifndef __cpp_lib_byteswap +# error "Feature-test macro for byteswap missing in " +#elif __cpp_lib_byteswap != 202110L +# error "Feature-test macro for byteswap has wrong value in " +#endif + +#include +#include +#include + +void +test01() +{ + static_assert( std::byteswap(0x12) == 0x12 ); + static_assert( std::byteswap(0x1234) == 0x3412 ); + static_assert( std::byteswap(0x12345678) == 0x78563412 ); + static_assert( std::byteswap(0x123456789abcdef0) + == static_cast(0xf0debc9a78563412) ); + static_assert( std::byteswap(0x21) == 0x21 ); + static_assert( std::byteswap(0x4321) == 0x2143 ); + static_assert( std::byteswap(0x87654321) == 0x21436587 ); + static_assert( std::byteswap(0xfedcba9876543210) + == static_cast(0x1032547698badcfe) ); +#if !defined(__STRICT_ANSI__) && defined __SIZEOF_INT128__ + constexpr __int128_t c1 = (static_cast<__int128_t>(0x0102030405060708) << 64 + | 0x090a0b0c0d0e0f10); + constexpr __int128_t c2 = (static_cast<__int128_t>(0x100f0e0d0c0b0a09) << 64 + | 0x0807060504030201); + constexpr __int128_t c3 = (static_cast<__int128_t>(0xf1e2d3c4b5a69788) << 64 + | 0x796a5b4c3d2e1f10); + constexpr __int128_t c4 = (static_cast<__int128_t>(0x101f2e3d4c5b6a79) << 64 + | 0x8897a6b5c4d3e2f1); + static_assert( std::byteswap(c1) == c2 ); + static_assert( std::byteswap(static_cast<__uint128_t>(c1)) + == static_cast<__uint128_t>(c2) ); + static_assert( std::byteswap(c3) == c4 ); +#endif + static_assert( std::byteswap(0xdeadbeef) == 0xefbeadde ); + static_assert( std::byteswap(0xdeadbeef) == 0xefbeadde ); + static_assert( std::byteswap(0xdeadbeef) + == static_cast(0xefbeadde) ); +} + +void +test02() +{ + volatile int8_t a = 0x12; + volatile int16_t b = 0x1234; + volatile int32_t c = 0x12345678; + volatile int64_t d = 0x123456789abcdef0; + volatile uint8_t e = 0x21; + volatile uint16_t f = 0x4321; + volatile uint32_t g = 0x87654321; + volatile uint64_t h = 0xfedcba9876543210; + VERIFY ( std::byteswap(a) == 0x12 ); + VERIFY ( std::byteswap(b) == 0x3412 ); + VERIFY ( std::byteswap(c) == 0x78563412 ); + VERIFY ( std::byteswap(d) == 0xf0debc9a78563412 ); + VERIFY ( std::byteswap(e) == 0x21 ); + VERIFY ( std::byteswap(f) == 0x2143 ); + VERIFY ( std::byteswap(g) == 0x21436587 ); + VERIFY ( std::byteswap(h) == 0x1032547698badcfe ); + VERIFY ( std::byteswap(std::byteswap(a)) == a ); + VERIFY ( std::byteswap(std::byteswap(b)) == b ); + VERIFY ( std::byteswap(std::byteswap(c)) == c ); + VERIFY ( std::byteswap(std::byteswap(d)) == d ); + VERIFY ( std::byteswap(std::byteswap(e)) == e ); + VERIFY ( std::byteswap(std::byteswap(f)) == f ); + VERIFY ( std::byteswap(std::byteswap(g)) == g ); + VERIFY ( std::byteswap(std::byteswap(h)) == h ); +#if !defined(__STRICT_ANSI__) && defined __SIZEOF_INT128__ + volatile __int128_t c1 = (static_cast<__int128_t>(0x0102030405060708) << 64 + | 0x090a0b0c0d0e0f10); + volatile __int128_t c2 = (static_cast<__int128_t>(0x100f0e0d0c0b0a09) << 64 + | 0x0807060504030201); + VERIFY ( std::byteswap(c1) == c2 ); + VERIFY ( std::byteswap<__uint128_t>(c1) == static_cast<__uint128_t>(c2) ); + VERIFY ( std::byteswap(std::byteswap(c1)) == c1 ); + VERIFY ( std::byteswap(std::byteswap<__uint128_t>(c2)) + == static_cast<__uint128_t>(c2) ); +#endif + VERIFY ( std::byteswap(0xdeadbeef) == 0xefbeadde ); + VERIFY ( std::byteswap(0xdeadbeef) == 0xefbeadde ); +} + +int main() +{ + test01(); + test02(); +} --- libstdc++-v3/testsuite/26_numerics/bit/bit.byteswap/version.cc.jj 2021-11-27 11:39:48.741024747 +0100 +++ libstdc++-v3/testsuite/26_numerics/bit/bit.byteswap/version.cc 2021-11-27 11:40:36.048355861 +0100 @@ -0,0 +1,27 @@ +// Copyright (C) 2021 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2b" } +// { dg-do compile { target c++23 } } + +#include + +#ifndef __cpp_lib_byteswap +# error "Feature-test macro for bit_cast missing in " +#elif __cpp_lib_byteswap != 202110L +# error "Feature-test macro for byteswap has wrong value in " +#endif Jakub