diff options
| -rw-r--r-- | libstdc++-v3/ChangeLog | 7 | ||||
| -rw-r--r-- | libstdc++-v3/include/bits/hashtable_policy.h | 7 | ||||
| -rw-r--r-- | libstdc++-v3/include/std/bit | 6 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc | 8 |
4 files changed, 24 insertions, 4 deletions
diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index a198549f0f3..98288521abd 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,5 +1,12 @@ 2018-08-30 Jonathan Wakely <jwakely@redhat.com> + * include/bits/hashtable_policy.h (__clp2): Fix calculation for LLP64 + targets where sizeof(size_t) > sizeof(long). Avoid undefined shifts + of the number of bits in the type. + * include/std/bit (__ceil2): Avoid undefined shifts. + * testsuite/26_numerics/bit/bit.pow.two/ceil2.cc: Test values with + the most signifiant bit set. + * config/abi/pre/gnu.ver: Add missing exports for mingw. * include/ext/pointer.h (_Pointer_adapter): Define operators for diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h index d7497711071..66fbfbe5f21 100644 --- a/libstdc++-v3/include/bits/hashtable_policy.h +++ b/libstdc++-v3/include/bits/hashtable_policy.h @@ -511,8 +511,11 @@ namespace __detail // Equivalent to return __n ? std::ceil2(__n) : 0; if (__n < 2) return __n; - return 1ul << (numeric_limits<unsigned long>::digits - - __builtin_clzl(__n - 1ul)); + const unsigned __lz = sizeof(size_t) > sizeof(long) + ? __builtin_clzll(__n - 1ull) + : __builtin_clzl(__n - 1ul); + // Doing two shifts avoids undefined behaviour when __lz == 0. + return (size_t(1) << (numeric_limits<size_t>::digits - __lz - 1)) << 1; } /// Rehash policy providing power of 2 bucket numbers. Avoids modulo diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit index 0aebac28758..bc2ade75b35 100644 --- a/libstdc++-v3/include/std/bit +++ b/libstdc++-v3/include/std/bit @@ -195,9 +195,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __ceil2(_Tp __x) noexcept { constexpr auto _Nd = numeric_limits<_Tp>::digits; - if (__x == 0) + if (__x == 0 || __x == 1) return 1; - return (_Tp)1u << (_Nd - std::__countl_zero((_Tp)(__x - 1u))); + const unsigned __n = _Nd - std::__countl_zero((_Tp)(__x - 1u)); + const _Tp __y_2 = (_Tp)1u << (__n - 1u); + return __y_2 << 1u; } template<typename _Tp> diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc index 65e1569c277..e41f82c8bb8 100644 --- a/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc +++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc @@ -55,6 +55,14 @@ test(UInt x) static_assert( std::ceil2(UInt(3) << 64) == (UInt(4) << 64) ); } + constexpr UInt msb = UInt(1) << (std::numeric_limits<UInt>::digits - 1); + static_assert( std::ceil2( msb ) == msb ); + // Larger values cannot be represented so the return value is unspecified, + // but must still be valid in constant expressions, i.e. not undefined. + static_assert( std::ceil2( UInt(msb + 1) ) != 77 ); + static_assert( std::ceil2( UInt(msb + 2) ) != 77 ); + static_assert( std::ceil2( UInt(msb + 77) ) != 77 ); + return true; } |