> My guess is they aim for convergence and it works well in practice but it's still unknown if that's guaranteed to be correct. I guess you refer only to the c

> My guess is they aim for convergence and it works well in practice but it's still unknown if that's guaranteed to be correct. I guess you refer only to the computation of transcendentals sin, exp, etc. (because even in native floating-point formats, most other individual operations are guaranteed to be rounded correctly). I haven't checked their docs carefully enough, but if it is like MPFR, the way they do it is by trading time guarantee for precision guarantee. So they can't predict how long each operation will take (let alone guarantee that it will go fast), so that they can guarantee that they meet your required precision.