[Bug libstdc++/110860] New: std::format("{:f}",2e304) invokes undefined behaviour

["gcc at pauldreik dot se" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110860

            Bug ID: 110860
           Summary: std::format("{:f}",2e304) invokes undefined behaviour
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at pauldreik dot se
  Target Milestone: ---

The following program, compiled with gcc 13.2:

#include <format>
#include <cstdio>

int main() {
std::puts(std::format("{:f}",2e304).c_str());
}

causes ubsan to warn:
/opt/compiler-explorer/gcc-13.2.0/include/c++/13.2.0/format:1489:52: runtime
error: negation of -2147483648 cannot be represented in type 'int'; cast to an
unsigned type to negate this value to itself

I believe the problem is using __builtin_abs() which uses integer, but is fed a
double.


Link to reproducer:

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