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author | Patrick Palka <ppalka@redhat.com> | 2023-04-24 13:39:54 -0400 |
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committer | Patrick Palka <ppalka@redhat.com> | 2023-05-12 11:16:38 -0400 |
commit | 22b86ea01b2a4902bb8ec5c5d0bef89aea67079c (patch) | |
tree | 0643afffc4a983ea98a8b3b28aa0d2ae9d4edad2 | |
parent | 794eb5742226d13ffec4431bdee510e8aebc8001 (diff) | |
download | gcc-22b86ea01b2a4902bb8ec5c5d0bef89aea67079c.tar.gz |
libstdc++: Fix __max_diff_type::operator>>= for negative values
This patch fixes sign bit propagation when right-shifting a negative
__max_diff_type value by more than one, a bug that our existing test
coverage didn't expose until r14-159-g03cebd304955a6 fixed the front
end's 'signed typedef-name' handling that the test relies on (which is
a non-standard extension to the language grammar).
libstdc++-v3/ChangeLog:
* include/bits/max_size_type.h (__max_diff_type::operator>>=):
Fix propagation of sign bit.
* testsuite/std/ranges/iota/max_size_type.cc: Avoid using the
non-standard 'signed typedef-name'. Add some compile-time tests
for right-shifting a negative __max_diff_type value by more than
one.
(cherry picked from commit 83470a5cd4c3d233e1d55b5e5553e1b9c553bf28)
-rw-r--r-- | libstdc++-v3/include/bits/max_size_type.h | 3 | ||||
-rw-r--r-- | libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc | 12 |
2 files changed, 12 insertions, 3 deletions
diff --git a/libstdc++-v3/include/bits/max_size_type.h b/libstdc++-v3/include/bits/max_size_type.h index 153b1bff5f4..d6cdb72662e 100644 --- a/libstdc++-v3/include/bits/max_size_type.h +++ b/libstdc++-v3/include/bits/max_size_type.h @@ -559,7 +559,8 @@ namespace ranges // Arithmetic right shift. const auto __msb = _M_rep._M_msb; _M_rep >>= __r._M_rep; - _M_rep._M_msb |= __msb; + if (__msb) + _M_rep |= ~(__max_size_type(-1) >> __r._M_rep); return *this; } diff --git a/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc b/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc index 983bdfbdaa6..5130447103f 100644 --- a/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc +++ b/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc @@ -25,8 +25,14 @@ using max_size_t = std::ranges::__detail::__max_size_type; using max_diff_t = std::ranges::__detail::__max_diff_type; using rep_t = max_size_t::__rep; +#if __SIZEOF_INT128__ +using signed_rep_t = __int128; +#else +using signed_rep_t = long long; +#endif static_assert(sizeof(max_size_t) == sizeof(max_diff_t)); +static_assert(sizeof(rep_t) == sizeof(signed_rep_t)); static_assert(std::regular<max_size_t>); static_assert(std::totally_ordered<max_size_t>); @@ -53,6 +59,8 @@ test01() static_assert(max_diff_t(3) % -2 == 1); static_assert(max_diff_t(-3) << 1 == -6); static_assert(max_diff_t(-3) >> 1 == -2); + static_assert(max_diff_t(-3) >> 2 == -1); + static_assert(max_diff_t(-3) >> 10 == -1); static_assert(max_diff_t(3) >> 1 == 1); static_assert(max_diff_t(3) >> 2 == 0); @@ -187,7 +195,7 @@ template<bool signed_p, bool shorten_p> void test02() { - using hw_type = std::conditional_t<signed_p, signed rep_t, rep_t>; + using hw_type = std::conditional_t<signed_p, signed_rep_t, rep_t>; using max_type = std::conditional_t<signed_p, max_diff_t, max_size_t>; using shorten_type = std::conditional_t<shorten_p, hw_type, max_type>; const int hw_type_bit_size = sizeof(hw_type) * __CHAR_BIT__; @@ -245,7 +253,7 @@ template<bool signed_p, bool toggle_base_p> void test03() { - using hw_type = std::conditional_t<signed_p, signed rep_t, rep_t>; + using hw_type = std::conditional_t<signed_p, signed_rep_t, rep_t>; using max_type = std::conditional_t<signed_p, max_diff_t, max_size_t>; using base_type = std::conditional_t<toggle_base_p, hw_type, max_type>; constexpr int hw_type_bit_size = sizeof(hw_type) * __CHAR_BIT__; |