Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!mcsun!sunic!draken!d88-jwa
From: d88-jwa@nada.kth.se (Jon Watte)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How to Cosine: some results
Message-ID: <2304@draken.nada.kth.se>
Date: 13 Nov 89 21:33:02 GMT
References: <2256@hudson.acc.virginia.edu>
Reply-To: d88-jwa@nada.kth.se (Jon W{tte)
Organization: Royal Institute of Technology, Stockholm, Sweden
Lines: 50

In article <2256@hudson.acc.virginia.edu> cak3g@astsun7.astro.Virginia.EDU (Colin Klipsch) writes:

    (WARNING: Assembly language discussion ahead!  Run for your lives!!)

Various ramblings deleted

    II) Table with quadratic interpolation:  Quadratic because linear
    interpolation would require too many table entries for 30b accuracy.

[...]

    the largest you can get away with.)  The primary disadvantage of this
    subroutine is that it requires a table with over a thousand entries,
    which amounts to over 4kB.  I note also that this routine makes use
    of the long multiply instructions on the 68020, which are unavailable
    on the 68000.

[...]

    IV) Call the M68881:  Convert the angle to radians in M68881
    format (96b), call FSINCOS, convert the result to fract.  Call FSINCOS
    because we need both sine and cosine in the transformation matrix
    anyway.  The fact that this calculates both will be taken into account.

[...]

    And the results:
     II)  Quadratic interp   1,250,297      79,981       24,100
     IV)  M68881 (FSINCOS)     817,654     122,301       66,400  (33,200)


Hey, are you running a Mac 128K or what ? 4kB for speed FASTER than a
Mc68881 ? That's NOTHING at all ! And consider; more people have the
68020 (or -30) than have the 68881 (or -2)

Probably those 4kB will be less than an average "about" box 8)

You could have the table in a resource (hell, you could have
EIGHT tables in a resource 8) and load it only when you need it,
if you're so concerned for memory. This would also save you the
trouble of feeding the data by hand to the program editor :-)

All in all, you have produced a VERY GOOD post (maybe my candidate
for "post of the year" :-) and the Net should have more of these...

Happy Hacking !
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