On Tue, 25 Apr 2006, Peter Onion wrote:

> On Tue, 2006-04-25 at 09:22 -0700, jshayden wrote:
>> Using the c18 libraries, does anyone have an example of using the math
>> functions in math.h.  I'm am getting trash output.  I thought it returned
>> IEEE floating point, but it doesn't appear to.  Not even the sign bit is
>> correct.  Here is a basic example I've tried working with.
>>
>> #include <p18f4680.h>
>> #include <math.h>
>>
>> void main(void)
>> {
>>
>> float_t x = 3.14;
>> float_t z;
>>
>> z = cos(x);
>>
>> }
>>
>>
>> z's output is as follows...
>> 00110110 11010110 11111011 00010110
>> ...which is nowhere close to -1.
>
> What do you expect to see for -1 ?   In a floating point format I would
> expect to see something representing -0.5 * 2^1   (2^1 being 2 raised to
> the power 1).

That's not the point. All the trig math functions expect radian input. 
E.g. try:

 	float_t pi;

 	pi = atan(1) * 4.0;

 	z = cos( pi / 4.0 );
 	...

A suitable constant for pi is defined somewhere (in math,h) as M_PI 
afair.

Peter



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