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From: grunwald@uiucdcsm.UUCP
Newsgroups: comp.arch
Subject: Cordic chips
Message-ID: <3300001@uiucdcsm>
Date: Mon, 30-Mar-87 11:19:00 EST
Article-I.D.: uiucdcsm.3300001
Posted: Mon Mar 30 11:19:00 1987
Date-Received: Fri, 3-Apr-87 06:30:08 EST
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Nf-ID: #N:uiucdcsm:3300001:000:1149
Nf-From: uiucdcsm.cs.uiuc.edu!grunwald    Mar 30 10:19:00 1987


In the discussion on str* & friends, someone mentioned using the CORDIC
routines for determining sin & cos at the same time.

This reminded me of a chip that a friend designed for a class project: a
general CORDIC processor, allowing you to set all the registers, turn the
crank and then extract the results.

	The wonderful thing was, not only do you get sin and cos for the
cost of a single function, several graphics applications can be sped up
dramatically by realising that CORDIC is simply rotating vectors.

	Instead of doing vector rotation by computing sin and cos, and then
doing all the multiplication by the rotation arrays, you simply put your
vector in the CORDIC unit, plug in the theta and out pops the rotated
vector. Rotating in 2 dimensions is as simple, you just rotate in X-Y plane
first and then the Y-Z plane.
	If I recall, addition of a few bells provides a way to determine
normal/tangent vectors rather quickly (which would seem useful for shading)

	Do any common FPU's use the CORDIC method for builtins? Are there any
ways to access the CORDIC registers directly?

Dirk Grunwald
Univ. of Illinois
grunwald@m.cs.uiuc.edu