Type Alias LogTailPolicy 

pub type LogTailPolicy<P> = ExtraPrecision<ExtraPrecision<P>>;

The policy the tail arms evaluate erfcx under: two precision rungs above the caller’s, so the default tier takes the full N = 40 Weideman table.

The log absorbs erfcx’s relative error as an absolute one against a result of -x^2/2, which is why the bump is affordable and why the tail can start as early as u = 4. Public so that Dual’s derivative factor, an erfcx quotient, can match.

Aliased Type

pub struct LogTailPolicy<P>(/* private fields */);