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Message-ID: <20240811200812.GZ3766212@port70.net>
Date: Sun, 11 Aug 2024 22:08:12 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: Damian McGuckin <damianm@....com.au>
Cc: MUSL <musl@...ts.openwall.com>
Subject: Re: catan(z)
* Damian McGuckin <damianm@....com.au> [2024-08-12 00:01:01 +1000]:
>
> In this routine, there are 2 lines of code
>
> t = 0.5 * atan2(2.0 * x, a);
> w = _redupi(t);
>
> The first computes atan2() which returns a number in the range [-pi,+pi]
> which means that t is a number in the range [-pi/2,+pi/2].
>
> As far as I understand, the routine _redupi(t) accepts a argument and
> reduces it into the range [-pi, +pi]. Am I mistaken?
*reduces into [-pi/2, pi/2]
>
> If I am not wrong, and 't' is already in the range that _redupi(t) will
> return, then _redupi() just returns its argument (within a rounding error).
> So it seems like a no-op to me.
>
> Can anybody comment?
it only changes the endpoints (t=+-pi/2 case) otherwise no-op
i dont know if we care about the endpoints but even if we do
there are better ways to fix them up
i think _redupi can be removed, nice catch.
>
> The routine is originally from Moshier's Cephes library. I have Moshier's
> book but I cannot find any hints there.
>
> Thanks - Damian
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