From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Sun,  2 Oct 2011 18:38:00 +0200
From: tlaronde@polynum.com
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Message-ID: <20111002163800.GA12773@polynum.com>
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Subject: [9fans] circular fonctions: precision?
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Hello,

Is there some documentation about the precision of the circular (i.e
trigonometric) fonctions, depending on the (plan9) implementation and
the hardware?

To my limited knowledge, an OS is integer based, so the floating
point support is mainly "user space" and is, despite IEEE754 and due to
the interaction between hardware, software, and programmer, really
floating, but is there a range given for the association of OS/hardware
telling that say sin(r) or asin(s) is accurate, at worst, at some
epsilon near?

To give a context, say you have arcs connected to nodes, and each node
has information about its connected arcs sorted by angle (2D). If I
want to
find the "straightest" arc continuing arc A through node N, I look for
an arc B so that the angle between A and B is nearest to M_PI. But if
the angles (from the node) had been computed by some circular fonction,
even two originally "straight" arcs may present an angle not exactly
M_PI, due to precision. Hence the question.

Cheers,
--
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                      http://www.kergis.com/
Key fingerprint = 0FF7 E906 FBAF FE95 FD89  250D 52B1 AE95 6006 F40C