[Bug libstdc++/124882] limit memchr count in char_traits::find

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124882

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This function is performance critical, adding a branch to deal with a condition
that's impossible in correct code doesn't seem desirable.

Maybe __n &= __PTRDIFF_MAX__ would be better, although still redundant in
correct code.