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Date: Tue, 11 Feb 2020 21:00:23 -0500
From: Rich Felker <>
Subject: Re: casinh function accuracy problem

On Wed, Feb 12, 2020 at 11:46:08AM +1100, Damian McGuckin wrote:
> On Tue, 11 Feb 2020, Rich Felker wrote:
> >High-quality complex math functions are a long-term wishlist item for
> >musl but nobody has stepped up to do them and I don't really feel like
> >doing it, at least not over other improvements I could be working on.
> As you say, they do work reasonably well even now.
> With even complex arithmetic being "unspecified" in IEEE-754-2019,
> it is an interesting issue where "interesting" does not have the
> conventional English sense of being a positive thing.
> >This might be an area well-served by sponsored enhancement if there's
> >a user who needs them improved with resources to pay someone to do it.
> Depending on your definition of "improved", it is anything from a
> big task to a huge task.
> And sadly, I have other things on my plate too.

My minimal criterion for large-scale improvements of src/complex would
be fixing any remaining cases where inf/nan behavior is badly wrong or
there's catastrophic error (>2^52 ulp, or even just >2^20 ulp or so).
Beyond that, I think "reducing ulp error" would be nice but hard to
quantify and make a goal without having an idea how bad it is now, not
to mention without having rigorous error bounds on the real math
library functions.


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