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| author | Jonathan Wakely <jwakely@redhat.com> | 2018-08-30 16:07:35 +0100 |
|---|---|---|
| committer | Jonathan Wakely <redi@gcc.gnu.org> | 2018-08-30 16:07:35 +0100 |
| commit | 2fb17d2d901d904479fa22dd01b887ff5bc48248 (patch) | |
| tree | 111035d748bf025dcc5d4a417edde0802112332d /libstdc++-v3/include/std/bit | |
| parent | 2ebbdb6ca3f69cdac97aeba48a7f00ea40337cd5 (diff) | |
| download | gcc-2fb17d2d901d904479fa22dd01b887ff5bc48248.zip gcc-2fb17d2d901d904479fa22dd01b887ff5bc48248.tar.gz gcc-2fb17d2d901d904479fa22dd01b887ff5bc48248.tar.bz2 | |
Avoid undefined shifts in ceil2 operations
For values where the result cannot be represented the shift width would
be equal to the width of the type, which is undefined. Perform two
well-defined shifts instead of one possible undefined shift.
* 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.
From-SVN: r263986
Diffstat (limited to 'libstdc++-v3/include/std/bit')
| -rw-r--r-- | libstdc++-v3/include/std/bit | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/libstdc++-v3/include/std/bit b/libstdc++-v3/include/std/bit index 0aebac2..bc2ade7 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> |