[Bug libstdc++/117406] std::ilogb should return INT_MAX when argument is infinite also for 16-bit floats

[pkeir at outlook dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117406

--- Comment #2 from Paul Keir <pkeir at outlook dot com> ---
Created attachment 59519
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59519&action=edit
Test for the proposed fix.