Path: utzoo!mnetor!uunet!husc6!mailrus!ames!pasteur!ucbvax!dewey.soe.berkeley.edu!robinson
From: robinson@dewey.soe.berkeley.edu (Michael Robinson)
Newsgroups: comp.sys.m68k
Subject: Re: assembly sine function
Message-ID: <23575@ucbvax.BERKELEY.EDU>
Date: 11 Apr 88 03:57:07 GMT
References: <2514@umd5.umd.edu> <9887@tekecs.TEK.COM> <4872@ecsvax.UUCP>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: robinson@dewey.soe.berkeley.edu.UUCP (Michael Robinson)
Organization: School of Education, UC-Berkeley
Lines: 26

In article <4872@ecsvax.UUCP> urjlew@ecsvax.UUCP (Rostyk Lewyckyj) writes:
<In article <9887@tekecs.TEK.COM>, andrew@frip.gwd.tek.com (Andrew Klossner) writes:
<> 	"does anyone out there have a PD sine/cosine function written
<> 	in 68000 assembly language?  I need one that will be VERY fast,
<> 	for it will be called durring an interrupt (VBLANK)."
<> 
<> I've got a very fast function: table lookup.  For example, if you can
<> round the argument to the nearest degree, then a 90-element table
<> suffices.  If you need seven-digit accuracy, a table won't help.
<
< If you don't get ready made code then I
<suggest using a table of sine(x) 0<=x<=pi/2 with a Taylor's series
<expansion for interpolation between tabulated values.  

If the prospect of calculating a Taylor series during a VBLANK is 
unappealing, you can do a simple first derivative interpolation using
the very same table, and the identities, sin' = cos and cos' = -sin.

With a 256 entry table, that should give you many bits of accuracy
quickly.

I hope you're using fixed point.

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Michael Robinson                              USENET:  ucbvax!ernie!robinson
                                              ARPA: robinson@ernie.berkeley.edu