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'[PIC] tan function on a 8 bit PIC'
2008\08\27@115758
by
alan smith
I did some searching, and saw some routines on arctan, but wondering is doing a tan calculation out the the reach of a 18F processor. What I am eventually implementing is audio eq calculations.
2008\08\27@122551
by
Walter Banks
Alan,
About a year ago I wrote a fixed point transcendental library.
It is not a problem to calculate tan on a micro including the
18F but I would avoid using it if it is possible to use a
separate algorithm in applications.
w..
alan smith wrote:
> I did some searching, and saw some routines on arctan, but wondering is doing a tan calculation out the the reach of a 18F processor. What I am eventually implementing is audio eq calculations.
2008\08\27@123024
by
John Temples
On Wed, 27 Aug 2008, alan smith wrote:
> I did some searching, and saw some routines on arctan, but wondering is doing a tan calculation out the the reach of a 18F processor. What I am eventually implementing is audio eq calculations.
HiTech PICC18 using 24bit floats:
#include <math.h>
void main(void)
{
float x, y;
x = tan(y);
}
Memory Summary:
Program space used 947h ( 2375) of 20000h bytes ( 1.8%)
Data space used 43h ( 67) of F00h bytes ( 1.7%)

John W. Temples, III
2008\08\27@125151
by
Dario Greggio
alan smith wrote:
> I did some searching, and saw some routines on arctan, but wondering is doing a tan calculation out the the reach of a 18F processor. What I am eventually implementing is audio eq calculations.
Could you look into C18 SRC folder?

Ciao, Dario
2008\08\27@131114
by
sergio masci
On Wed, 27 Aug 2008, alan smith wrote:
> I did some searching, and saw some routines on arctan, but wondering is
> doing a tan calculation out the the reach of a 18F processor. What I am
> eventually implementing is audio eq calculations.
Yes you can calculate tan on an 18F. I guess the real question is how fast
do you need to calculate it.
I've written a floating point tan library function for the XCSB compiler
and that generates code for the dumber 16F.
Regards
Sergio Masci
2008\08\27@131533
by
A K
You can approximate via interpolation and a discrete TAN lookup table
rather quickly.
sergio masci wrote:
{Quote hidden}>
> On Wed, 27 Aug 2008, alan smith wrote:
>
>> I did some searching, and saw some routines on arctan, but wondering is
>> doing a tan calculation out the the reach of a 18F processor. What I am
>> eventually implementing is audio eq calculations.
>
> Yes you can calculate tan on an 18F. I guess the real question is how fast
> do you need to calculate it.
>
> I've written a floating point tan library function for the XCSB compiler
> and that generates code for the dumber 16F.
>
> Regards
> Sergio Masci
2008\08\27@131917
by
peter green
alan smith wrote:
> I did some searching, and saw some routines on arctan, but wondering is doing a tan calculation out the the reach of a 18F processor.
It will certainly be able to do it. Whether it will be able to do it at
the speed and accuracy that your application requires is another matter.
2008\08\27@141152
by
Scott Dattalo
> I did some searching, and saw some routines on arctan, but wondering is
> doing a tan calculation out the the reach of a 18F processor. What I am
> eventually implementing is audio eq calculations.
Hi Alan,
Why do you specifically need to calculate tan()?
You might get away with the approximation:
tan(x) ~ x for small x
But if you need to calculate all the way out to tan(pi/2), you're in for a
surprise!
Scott
2008\08\27@153518
by
alan smith

Yep...come to the conclusion that the lil ol 18F won't cut it. True I can use a look up table, but I found an easier method....find a part that has things built in, in as much as the function I need for the audio eq. Wolfson has a part, and yes it limits the choice of centre frequencies I can choose, for this particular app it will fit just fine.
Thanks for the replies
 On Wed, 8/27/08, Scott Dattalo <spam_OUTscottTakeThisOuTdattalo.com> wrote:
{Quote hidden}> From: Scott Dattalo <
.....scottKILLspam@spam@dattalo.com>
> Subject: Re: [PIC] tan function on a 8 bit PIC
> To: "Microcontroller discussion list  Public." <
piclistKILLspammit.edu>
> Date: Wednesday, August 27, 2008, 11:11 AM
> > I did some searching, and saw some routines on arctan,
> but wondering is
> > doing a tan calculation out the the reach of a 18F
> processor. What I am
> > eventually implementing is audio eq calculations.
>
> Hi Alan,
>
> Why do you specifically need to calculate tan()?
>
> You might get away with the approximation:
>
> tan(x) ~ x for small x
>
> But if you need to calculate all the way out to tan(pi/2),
> you're in for a
> surprise!
>
> Scott
> 
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