[Bug libstdc++/115399] std::tr2::dynamic_bitset shift behaves differently from std::bitset

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115399

Jonathan Wakely  changed:

   What|Removed |Added

 Resolution|--- |FIXED
 Status|ASSIGNED|RESOLVED
   Target Milestone|--- |15.0

--- Comment #5 from Jonathan Wakely  ---
Fixed on trunk. I'll probably backport it to the release branches at some
point.

[Bug libstdc++/115399] std::tr2::dynamic_bitset shift behaves differently from std::bitset

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115399

--- Comment #4 from GCC Commits  ---
The master branch has been updated by Jonathan Wakely :

https://gcc.gnu.org/g:bd3a312728fbf8c35a09239b9180269f938f872e

commit r15-1213-gbd3a312728fbf8c35a09239b9180269f938f872e
Author: Jonathan Wakely 
Date:   Mon Jun 10 14:08:16 2024 +0100

libstdc++: Fix std::tr2::dynamic_bitset shift operations [PR115399]

The shift operations for dynamic_bitset fail to zero out words where the
non-zero bits were shifted to a completely different word.

For a right shift we don't need to sanitize the unused bits in the high
word, because we know they were already clear and a right shift doesn't
change that.

libstdc++-v3/ChangeLog:

PR libstdc++/115399
* include/tr2/dynamic_bitset (operator>>=): Remove redundant
call to _M_do_sanitize.
* include/tr2/dynamic_bitset.tcc (_M_do_left_shift): Zero out
low bits in words that should no longer be populated.
(_M_do_right_shift): Likewise for high bits.
* testsuite/tr2/dynamic_bitset/pr115399.cc: New test.

[Bug libstdc++/115399] std::tr2::dynamic_bitset shift behaves differently from std::bitset

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115399

Jonathan Wakely  changed:

   What|Removed |Added

   Keywords||wrong-code
   Assignee|unassigned at gcc dot gnu.org  |redi at gcc dot gnu.org
 Status|NEW |ASSIGNED

[Bug libstdc++/115399] std::tr2::dynamic_bitset shift behaves differently from std::bitset

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115399

Jonathan Wakely  changed:

   What|Removed |Added

   Last reconfirmed||2024-06-10
 Ever confirmed|0   |1
 Status|UNCONFIRMED |NEW

--- Comment #3 from Jonathan Wakely  ---
The tr2 extensions never even got proposed for standardization and are not in
any ISO document at all. They're not well tested and nobody uses them.

[Bug libstdc++/115399] std::tr2::dynamic_bitset shift behaves differently from std::bitset

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115399

Andrew Pinski  changed:

   What|Removed |Added

   See Also||https://gcc.gnu.org/bugzill
   ||a/show_bug.cgi?id=114498

--- Comment #2 from Andrew Pinski  ---
Note I think std::tr2 should be deprecated in a similar way as std::tr1 is
being considered.

[Bug libstdc++/115399] std::tr2::dynamic_bitset shift behaves differently from std::bitset

[adamant.pwn at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115399

--- Comment #1 from Oleksandr Kulkov  ---
The bug also affects right shift for a similar reason
(https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/tr2/dynamic_bitset.tcc#L91):

#include 
#include 
#include 
#include 

int main() {
std::tr2::dynamic_bitset<> test(128);
for (int i = 64; i < 128; i++) test[i] = 1;
std::cout << test << "\n";
std::cout << (test >> 65) << "\n\n";

boost::dynamic_bitset<> test2(128);
for (int i = 64; i < 128; i++) test2[i] = 1;
std::cout << test2 << "\n";
std::cout << (test2 >> 65) << "\n\n";

std::bitset<128> test3;
for (int i = 64; i < 128; i++) test3[i] = 1;
std::cout << test3 << "\n";
std::cout << (test3 >> 65) << "\n\n";
}

Output:


0111


0111


0111

See also https://github.com/emsr/tr2/issues/1.