This proposal has now been accepted for C++20, with a few changes. This patch adjusts std::rotl and std::rotr to match the final specification and declares the additions for C++2a mode even when __STRICT_ANSI__ is defined.
* include/std/bit (__rotl, __rotr): Change second parameter from unsigned int to int and handle negative values. (rotl, rotr): Remove check for __STRICT_ANSI__. Change second parameter from unsigned int to int. Add nodiscard attribute. * testsuite/26_numerics/bit/bitops.rot/rotl.cc: Rename to ... * testsuite/26_numerics/bit/bit.rotate/rotl.cc: Here. Test negative shifts. * testsuite/26_numerics/bit/bitops.rot/rotr.cc: Rename to ... * testsuite/26_numerics/bit/bit.rotate/rotr.cc: Here. Test negative shifts. Tested x86_64-linux, committed to trunk. I'll backport this to gcc-9-branch too.
commit b58d3908b4fcf83343f93bba8c4f5e49e982b894 Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4> Date: Mon Jul 22 16:53:36 2019 +0000 Adjust std::rotl, std::rotr etc to match final P0553R4 proposal This proposal has now been accepted for C++20, with a few changes. This patch adjusts std::rotl and std::rotr to match the final specification and declares the additions for C++2a mode even when __STRICT_ANSI__ is defined. * include/std/bit (__rotl, __rotr): Change second parameter from unsigned int to int and handle negative values. (rotl, rotr): Remove check for __STRICT_ANSI__. Change second parameter from unsigned int to int. Add nodiscard attribute. * testsuite/26_numerics/bit/bitops.rot/rotl.cc: Rename to ... * testsuite/26_numerics/bit/bit.rotate/rotl.cc: Here. Test negative shifts. * testsuite/26_numerics/bit/bitops.rot/rotr.cc: Rename to ... * testsuite/26_numerics/bit/bit.rotate/rotr.cc: Here. Test negative shifts. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@273706 138bc75d-0d04-0410-961f-82ee72b054a4 diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit index d019b1ee600..f17d2f1bd59 100644 --- a/libstdc++-v3/include/std/bit +++ b/libstdc++-v3/include/std/bit @@ -42,20 +42,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template<typename _Tp> constexpr _Tp - __rotl(_Tp __x, unsigned int __s) noexcept + __rotl(_Tp __x, int __s) noexcept { constexpr auto _Nd = numeric_limits<_Tp>::digits; - const unsigned __sN = __s % _Nd; - return (__x << __sN) | (__x >> ((_Nd - __sN) % _Nd)); + const int __r = __s % _Nd; + if (__r == 0) + return __x; + else if (__r > 0) + return (__x << __r) | (__x >> ((_Nd - __r) % _Nd)); + else + return (__x >> -__r) | (__x << ((_Nd + __r) % _Nd)); // rotr(x, -r) } template<typename _Tp> constexpr _Tp - __rotr(_Tp __x, unsigned int __s) noexcept + __rotr(_Tp __x, int __s) noexcept { constexpr auto _Nd = numeric_limits<_Tp>::digits; - const unsigned __sN = __s % _Nd; - return (__x >> __sN) | (__x << ((_Nd - __sN) % _Nd)); + const int __r = __s % _Nd; + if (__r == 0) + return __x; + else if (__r > 0) + return (__x >> __r) | (__x << ((_Nd - __r) % _Nd)); + else + return (__x << -__r) | (__x >> ((_Nd + __r) % _Nd)); // rotl(x, -r) } template<typename _Tp> @@ -244,20 +254,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION using _If_is_unsigned_integer = enable_if_t<__is_unsigned_integer<_Tp>::value, _Up>; -#if ! __STRICT_ANSI__ - // [bitops.rot], rotating + // [bit.rot], rotating template<typename _Tp> - constexpr _If_is_unsigned_integer<_Tp> - rotl(_Tp __x, unsigned int __s) noexcept + [[nodiscard]] constexpr _If_is_unsigned_integer<_Tp> + rotl(_Tp __x, int __s) noexcept { return std::__rotl(__x, __s); } template<typename _Tp> - constexpr _If_is_unsigned_integer<_Tp> - rotr(_Tp __x, unsigned int __s) noexcept + [[nodiscard]] constexpr _If_is_unsigned_integer<_Tp> + rotr(_Tp __x, int __s) noexcept { return std::__rotr(__x, __s); } - // [bitops.count], counting + // [bit.count], counting template<typename _Tp> constexpr _If_is_unsigned_integer<_Tp, int> @@ -283,9 +292,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION constexpr _If_is_unsigned_integer<_Tp, int> popcount(_Tp __x) noexcept { return std::__popcount(__x); } -#endif - // Integral power-of-two operations + // [bit.pow.two], integral powers of 2 template<typename _Tp> constexpr _If_is_unsigned_integer<_Tp, bool> diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bitops.rot/rotl.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotl.cc similarity index 89% rename from libstdc++-v3/testsuite/26_numerics/bit/bitops.rot/rotl.cc rename to libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotl.cc +++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotl.cc @@ -20,12 +20,27 @@ #include <bit> +template<typename UInt> +constexpr bool +test_negative_shifts() +{ + constexpr unsigned digits = std::numeric_limits<UInt>::digits; + + UInt xarr[] = { (UInt)-1, 0, 1, 3, 6, 7, 0x10, 0x11, 0x22, 0x44, 0x80 }; + int sarr[] = { 1, 4, 5, digits - 1, digits }; + for (UInt x : xarr) + for (int s : sarr) + if (std::rotl(x, -s) != std::rotr(x, s)) + return false; + return true; +} + template<typename UInt> constexpr auto test(UInt x) --> decltype(std::rotl(x, 0u)) +-> decltype(std::rotl(x, 0)) { - static_assert( noexcept(std::rotl(x, 0u)) ); + static_assert( noexcept(std::rotl(x, 0)) ); constexpr unsigned digits = std::numeric_limits<UInt>::digits; @@ -63,6 +78,8 @@ test(UInt x) static_assert( std::rotl((UInt)0b1010'0101, 4) == 0b1010'0101'0000 ); } + static_assert( test_negative_shifts<UInt>() ); + return true; } diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bitops.rot/rotr.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotr.cc similarity index 89% rename from libstdc++-v3/testsuite/26_numerics/bit/bitops.rot/rotr.cc rename to libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotr.cc +++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotr.cc @@ -20,12 +20,27 @@ #include <bit> +template<typename UInt> +constexpr bool +test_negative_shifts() +{ + constexpr unsigned digits = std::numeric_limits<UInt>::digits; + + UInt xarr[] = { (UInt)-1, 0, 1, 3, 6, 7, 0x10, 0x11, 0x22, 0x44, 0x80 }; + int sarr[] = { 1, 4, 5, digits - 1, digits }; + for (UInt x : xarr) + for (int s : sarr) + if (std::rotr(x, -s) != std::rotl(x, s)) + return false; + return true; +} + template<typename UInt> constexpr auto test(UInt x) --> decltype(std::rotr(x, 0u)) +-> decltype(std::rotr(x, 0)) { - static_assert( noexcept(std::rotr(x, 0u)) ); + static_assert( noexcept(std::rotr(x, 0)) ); constexpr unsigned digits = std::numeric_limits<UInt>::digits; @@ -65,6 +80,8 @@ test(UInt x) == (0b1010 | ((UInt)0b0101 << digits - 4)) ); } + static_assert( test_negative_shifts<UInt>() ); + return true; }