> There's one more optimization that can be applied. Instead of computing
> (1+(y/x)^2) and using that as input to the lg(), it'd make more sense to
> compute (y/x) and create a new table that implements the function:
>
> f(w) = lg(1+w^2)
>
> This saves the squaring.
>
> A comment about the division: the ratio y/x will be less than 1 ( or it
> should be less than 1, if it's not then factor out y instead of x). If you
> performed an 8-bit integer division, you'll get zero. You could perform a
> 16-bit/8-bit division and premultiply y by 0x100 (i.e. move it to the
> upper byte of a 16-bit word). However a slightly more efficient division
> can be found in the arctan routine:
>
> http://www.dattalo.com/technical/software/pic/arctan.asm
>
> Look for FRAC_DIV:, a "fractional division" routine.
>
> Also, the coefficients in the above equations can be factored into the
> tables. When all's said done, this equation should take less than 200
> cycles to compute.
>
> Scott

Thanks Scott I will look at that.  I appreciate the help.  I am not a
complete novice with the PIC but this one is really stretching me.  I can't
help thinking there must be an easier way to add two non linear values!

David

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body