libstdc++: Implement std::byteswap for C++23
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.
2021-11-28 Jakub Jelinek <jakub@redhat.com>
* 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.
This commit is contained in:
Jakub Jelinek
parent
7a66c4909f
commit
7393fa8b1d
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@ -78,6 +78,55 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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}
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#endif
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#if __cplusplus > 202002L
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#define __cpp_lib_byteswap 202110L
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/// Reverse order of bytes in the object representation of `value`.
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template<typename _Tp>
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constexpr enable_if_t<is_integral<_Tp>::value, _Tp>
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byteswap(_Tp __value) noexcept
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{
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if constexpr (sizeof(_Tp) == 1)
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return __value;
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#if __cpp_if_consteval >= 202106L && __CHAR_BIT__ == 8
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if !consteval
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{
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if constexpr (sizeof(_Tp) == 2)
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return __builtin_bswap16(__value);
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if constexpr (sizeof(_Tp) == 4)
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return __builtin_bswap32(__value);
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if constexpr (sizeof(_Tp) == 8)
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return __builtin_bswap64(__value);
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if constexpr (sizeof(_Tp) == 16)
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#if __has_builtin(__builtin_bswap128)
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return __builtin_bswap128(__value);
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#else
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return (__builtin_bswap64(__value >> 64)
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| (static_cast<_Tp>(__builtin_bswap64(__value)) << 64));
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#endif
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}
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#endif
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// Fallback implementation that handles even __int24 etc.
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using _Up = typename __make_unsigned<__remove_cv_t<_Tp>>::__type;
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size_t __diff = __CHAR_BIT__ * (sizeof(_Tp) - 1);
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_Up __mask1 = static_cast<unsigned char>(~0);
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_Up __mask2 = __mask1 << __diff;
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_Up __val = __value;
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for (size_t __i = 0; __i < sizeof(_Tp) / 2; ++__i)
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{
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_Up __byte1 = __val & __mask1;
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_Up __byte2 = __val & __mask2;
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__val = (__val ^ __byte1 ^ __byte2
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^ (__byte1 << __diff) ^ (__byte2 >> __diff));
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__mask1 <<= __CHAR_BIT__;
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__mask2 >>= __CHAR_BIT__;
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__diff -= 2 * __CHAR_BIT__;
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}
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return __val;
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}
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#endif
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/// @cond undoc
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template<typename _Tp>
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@ -294,6 +294,7 @@
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#if __cplusplus > 202002L
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// c++2b
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#define __cpp_lib_adaptor_iterator_pair_constructor 202106L
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#define __cpp_lib_byteswap 202110L
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#define __cpp_lib_invoke_r 202106L
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#define __cpp_lib_is_scoped_enum 202011L
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#if __cpp_lib_concepts
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@ -0,0 +1,112 @@
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// Copyright (C) 2021 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-options "-std=gnu++2b" }
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// { dg-do compile { target c++23 } }
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#include <bit>
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#ifndef __cpp_lib_byteswap
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# error "Feature-test macro for byteswap missing in <bit>"
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#elif __cpp_lib_byteswap != 202110L
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# error "Feature-test macro for byteswap has wrong value in <bit>"
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#endif
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#include <cstdint>
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#include <cstring>
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#include <testsuite_hooks.h>
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void
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test01()
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{
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static_assert( std::byteswap<int8_t>(0x12) == 0x12 );
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static_assert( std::byteswap<int16_t>(0x1234) == 0x3412 );
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static_assert( std::byteswap<int32_t>(0x12345678) == 0x78563412 );
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static_assert( std::byteswap<int64_t>(0x123456789abcdef0)
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== static_cast<int64_t>(0xf0debc9a78563412) );
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static_assert( std::byteswap<uint8_t>(0x21) == 0x21 );
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static_assert( std::byteswap<uint16_t>(0x4321) == 0x2143 );
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static_assert( std::byteswap<uint32_t>(0x87654321) == 0x21436587 );
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static_assert( std::byteswap<uint64_t>(0xfedcba9876543210)
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== static_cast<uint64_t>(0x1032547698badcfe) );
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#if !defined(__STRICT_ANSI__) && defined __SIZEOF_INT128__
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constexpr __int128_t c1 = (static_cast<__int128_t>(0x0102030405060708) << 64
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| 0x090a0b0c0d0e0f10);
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constexpr __int128_t c2 = (static_cast<__int128_t>(0x100f0e0d0c0b0a09) << 64
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| 0x0807060504030201);
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constexpr __int128_t c3 = (static_cast<__int128_t>(0xf1e2d3c4b5a69788) << 64
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| 0x796a5b4c3d2e1f10);
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constexpr __int128_t c4 = (static_cast<__int128_t>(0x101f2e3d4c5b6a79) << 64
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| 0x8897a6b5c4d3e2f1);
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static_assert( std::byteswap(c1) == c2 );
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static_assert( std::byteswap(static_cast<__uint128_t>(c1))
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== static_cast<__uint128_t>(c2) );
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static_assert( std::byteswap(c3) == c4 );
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#endif
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static_assert( std::byteswap<const uint32_t>(0xdeadbeef) == 0xefbeadde );
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static_assert( std::byteswap<volatile uint32_t>(0xdeadbeef) == 0xefbeadde );
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static_assert( std::byteswap<int32_t>(0xdeadbeef)
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== static_cast<int32_t>(0xefbeadde) );
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}
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void
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test02()
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{
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volatile int8_t a = 0x12;
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volatile int16_t b = 0x1234;
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volatile int32_t c = 0x12345678;
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volatile int64_t d = 0x123456789abcdef0;
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volatile uint8_t e = 0x21;
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volatile uint16_t f = 0x4321;
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volatile uint32_t g = 0x87654321;
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volatile uint64_t h = 0xfedcba9876543210;
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VERIFY ( std::byteswap<int8_t>(a) == 0x12 );
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VERIFY ( std::byteswap<int16_t>(b) == 0x3412 );
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VERIFY ( std::byteswap(c) == 0x78563412 );
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VERIFY ( std::byteswap(d) == 0xf0debc9a78563412 );
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VERIFY ( std::byteswap<uint8_t>(e) == 0x21 );
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VERIFY ( std::byteswap<uint16_t>(f) == 0x2143 );
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VERIFY ( std::byteswap(g) == 0x21436587 );
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VERIFY ( std::byteswap(h) == 0x1032547698badcfe );
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VERIFY ( std::byteswap(std::byteswap<int8_t>(a)) == a );
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VERIFY ( std::byteswap(std::byteswap<int16_t>(b)) == b );
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VERIFY ( std::byteswap(std::byteswap(c)) == c );
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VERIFY ( std::byteswap(std::byteswap(d)) == d );
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VERIFY ( std::byteswap(std::byteswap<uint8_t>(e)) == e );
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VERIFY ( std::byteswap(std::byteswap<uint16_t>(f)) == f );
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VERIFY ( std::byteswap(std::byteswap(g)) == g );
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VERIFY ( std::byteswap(std::byteswap(h)) == h );
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#if !defined(__STRICT_ANSI__) && defined __SIZEOF_INT128__
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volatile __int128_t c1 = (static_cast<__int128_t>(0x0102030405060708) << 64
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| 0x090a0b0c0d0e0f10);
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volatile __int128_t c2 = (static_cast<__int128_t>(0x100f0e0d0c0b0a09) << 64
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| 0x0807060504030201);
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VERIFY ( std::byteswap(c1) == c2 );
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VERIFY ( std::byteswap<__uint128_t>(c1) == static_cast<__uint128_t>(c2) );
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VERIFY ( std::byteswap(std::byteswap(c1)) == c1 );
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VERIFY ( std::byteswap(std::byteswap<__uint128_t>(c2))
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== static_cast<__uint128_t>(c2) );
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#endif
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VERIFY ( std::byteswap<const uint32_t>(0xdeadbeef) == 0xefbeadde );
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VERIFY ( std::byteswap<volatile uint32_t>(0xdeadbeef) == 0xefbeadde );
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}
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int main()
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{
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test01();
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test02();
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}
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@ -0,0 +1,27 @@
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// Copyright (C) 2021 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-options "-std=gnu++2b" }
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// { dg-do compile { target c++23 } }
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#include <version>
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#ifndef __cpp_lib_byteswap
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# error "Feature-test macro for bit_cast missing in <version>"
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#elif __cpp_lib_byteswap != 202110L
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# error "Feature-test macro for byteswap has wrong value in <version>"
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#endif
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