`On Sun, Jul 10, 2005 at 12:48:30AM +0200, Peter Osterlund wrote:> Vojtech Pavlik <vojtech@suse.cz> writes:> > > Btw, what I don't completely understand is why you need linear> > regression, when you're not trying to detect motion or something like> > that. Basic floating average, or even simpler filtering like the input> > core uses for fuzz could work well enough I believe.> > Indeed, this function doesn't make much sense:> > +static inline int smooth_history(int x0, int x1, int x2, int x3)> +{> +	return x0 - ( x0 * 3 + x1 - x2 - x3 * 3 ) / 10;> +}> > In the X driver, a derivative estimate is computed from the last 4> absolute positions, and in that case the least squares estimate is> given by the factors [.3 .1 -.1 -.3]. However, in this case you want> to compute an absolute position estimate from the last 4 absolute> positions, and in this case the least squares estimate is given by the> factors [.25 .25 .25 .25], ie a floating average. If the function is> changed to this:> > +static inline int smooth_history(int x0, int x1, int x2, int x3)> +{> +	return (x0 + x1 + x2 + x3) / 4;> +}> > the standard deviation of the noise will be reduced by a factor of 2> compared to the unfiltered values. With the old smooth_history()> function, the noise reduction will only be a factor of 1.29.Using a function like	return (x_old * 3 + x) / 4;eliminates the need for a FIFO, and has similar (if not better)properties to floating average, because its coefficients are[ .25 .18 .14 .10 ... ].Setting	absfuzz[ABS_X] = some number;activates the abovementioned filtering (with additional cutoff and fastmotion compensation) directly in input.c, which should eliminate a lotof the code in the appletouch driver.-- Vojtech PavlikSuSE Labs, SuSE CR-To unsubscribe from this list: send the line "unsubscribe linux-kernel" inthe body of a message to majordomo@vger.kernel.orgMore majordomo info at  http://vger.kernel.org/majordomo-info.htmlPlease read the FAQ at  http://www.tux.org/lkml/`