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Message-ID: <alpine.LRH.2.02.1903181023100.25032@key0.esi.com.au>
Date: Mon, 18 Mar 2019 10:46:20 +1100 (AEDT)
From: Damian McGuckin <damianm@....com.au>
To: musl@...ts.openwall.com
Subject: Re: Re: atanhf(x) Slight Accuracy Improvements
On Mon, 18 Mar 2019, Szabolcs Nagy wrote:
> if you improve accuracy without performance loss that sounds useful, but
> i cannot comment on it without seeing the patch.
The main extra load is rather when computing
f = 2 * y + (2 * y * y) / (1 - y)
and
hfsq = (0.5 * f) * f
it is computed using a slightly different formula and then dissected like
(f-hfsq) is currently handled in log2.c because of the cancellation error
seen around sqrt(2), which in this case is when the absolute value
of the argument 'x', i.e. 'y' from MUSL's atanh.c,, has a value of
sqrt(2) - 1
-----------
sqrt(2) + 1
I need to work on the code because currently it does not conform to the
normal way MUSL is coded. That is somewhat because the C code was ported
from a research project which is using the Chapel language and has some
design consideration which are irrelevant to MUSL, and others which are
are more limiting than what MUSL has. It might take me a few weeks because
I have some other work priorities for the next 3 weeks and also need to
document the research results for the Chapel project first.
Regards - Damian
Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
Views & opinions here are mine and not those of any past or present employer
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