From f35da524a26d82cb1aa4a71ce48f92c64d506658 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Mon, 22 Jul 2019 17:53:36 +0100 Subject: [PATCH] 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. From-SVN: r273706 --- libstdc++-v3/ChangeLog | 11 ++++++ libstdc++-v3/include/std/bit | 38 +++++++++++-------- .../bit/{bitops.rot => bit.rotate}/rotl.cc | 21 +++++++++- .../bit/{bitops.rot => bit.rotate}/rotr.cc | 21 +++++++++- 4 files changed, 72 insertions(+), 19 deletions(-) rename libstdc++-v3/testsuite/26_numerics/bit/{bitops.rot => bit.rotate}/rotl.cc (89%) rename libstdc++-v3/testsuite/26_numerics/bit/{bitops.rot => bit.rotate}/rotr.cc (89%) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 4d163357f5a..6c6e41db802 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,5 +1,16 @@ 2019-07-22 Jonathan Wakely + * 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. + * include/std/bit (__ceil2): Make unrepresentable results undefined, as per P1355R2. Add debug assertion. Perform one left shift, not two, so that out of range values cause undefined behaviour. Ensure that 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 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 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 @@ -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 - 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 - 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 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 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 index 2d97ae8c465..dfceca071ae 100644 --- a/libstdc++-v3/testsuite/26_numerics/bit/bitops.rot/rotl.cc +++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotl.cc @@ -20,12 +20,27 @@ #include +template +constexpr bool +test_negative_shifts() +{ + constexpr unsigned digits = std::numeric_limits::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 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::digits; @@ -63,6 +78,8 @@ test(UInt x) static_assert( std::rotl((UInt)0b1010'0101, 4) == 0b1010'0101'0000 ); } + static_assert( test_negative_shifts() ); + 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 index c41c24d816a..f3bb94b1ef4 100644 --- a/libstdc++-v3/testsuite/26_numerics/bit/bitops.rot/rotr.cc +++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.rotate/rotr.cc @@ -20,12 +20,27 @@ #include +template +constexpr bool +test_negative_shifts() +{ + constexpr unsigned digits = std::numeric_limits::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 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::digits; @@ -65,6 +80,8 @@ test(UInt x) == (0b1010 | ((UInt)0b0101 << digits - 4)) ); } + static_assert( test_negative_shifts() ); + return true; } -- 2.30.2