It is not about being very close. IEEE says "Comparisons shall ignore the sign of zero" and erlang (or rather CPU instructions erlang outputs for float == float

It is not about being very close. IEEE says "Comparisons shall ignore the sign of zero" and erlang (or rather CPU instructions erlang outputs for float == float) respects that While =:= is not something mandated by IEEE. Erlang implements such an operator on floats and it decides to compare false for 0.0 & -0.0. So it probably compares bits/does integer comparisons on same data