Function libm_identity 

fn libm_identity() -> String

The C library the float bits above came from, as far as it can be read cheaply.

Best effort by design: this is a diagnostic on a comment line, not an input to any comparison, so an unknown answer is unknown libm rather than an error. ldd --version’s first line names glibc’s version on every glibc system and musl’s absence of one is itself informative.