sin()/cos()/tan() for kernel code? '_ 'a

Stephen Montgomery-Smith stephen at
Sun Feb 11 17:32:01 UTC 2007

On Sun, 11 Feb 2007, Daniel Eischen wrote:

> On Sun, 11 Feb 2007, Eugene M. Kim wrote:
>> Hello all,
>> I am writing a mouse device driver for my Wacom tablet (Intuos 2 9x12).
>> The tablet comes with a mouse and I managed to get valid coordinate data
>> from the device.  However, unlike usual mice, the coordinate system is
>> tied not to the orientation of the mouse itself, but to the tablet,
>> which acts much like a "mouse pad".  So, for example, if I rotate the
>> mouse 30 degrees to the left and move it left and right, the mouse
>> cursor would move not horizontally, but to 2- or 8-o'clock.
>> Fortunately the mouse also provides orientation data along with
>> coordinate data, so the correct cursor movement could be calculated from
>> it.  The problem: The calculation needs trigonometry, but there seems to
>> be no math library support in the kernel (I ran "grep -w cos" on the
>> -CURRENT source tree, which turned nothing up).
>> Does anyone have an idea on how to do this?
> Can't you do this in userland?  Teach moused?

Since you will only need sin and cos evaluated to the nearest degree, if 
that, I suggest a simple look up table.  There is also something called 
the CORDIC method, I think, but I suspect that the look up table will be 
so much easier to program, and negligable extra space overhead.


More information about the freebsd-hackers mailing list