Cordic algorithm troubles

[rawbus]

So I'm doing some digital signal processing. I have a a current and a voltage signal that I am multiplying together and then filtering through a lowpass filter to get a signal that equals A*B*cos(phi)/2. At this point I want to find phi, so I need the inverse cosine function.

Unfortunatly I'm having troubles trying to write a cordic algorithm because I'm confused starting with a polar coordinate system. Everything I've read only shows rectanglular coordinates. This is my first time doing any sort of dsp so I would appreciate any help or advice.

 

[alaparthi]

Cordic can be used in two modes:
Rotational Mode
Vectoring Mode

To compute, arcsine, use CORDIC algorithm in Vectoring mode, with the following initializations:
x0 = 1/An (Process Gain)
y0 = input (for which you need compute arcsine)
z0 = 0

To get arccosine, value use the above algo and adjust accordingly based on the quadrant.

Let me know if you have any questions.

 

[rawbus]

Ok, that helps alot. Thanks for the reply.

 

[Vladimir Baykov]

But for evaluation of ARCSIN and ARCCOS
you need use CORDIC with the "double iteration" !

http://groups.google.de/group/comp....93850cafff7a?hl=de&q=cordic+double+iterations

http://baykov.de/CORDIC1972.htm
http://baykov.de/Cordic1975.htm

http://www.umup.narod.ru/1115.zip