Re: atan2 and sqrt --> in driver

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> The driver is for the wii-remote, so get 1 byte for x-, y- and
>> z-axis.  Based on this values I will calculate the
>> pitch = atan2(y, sqrt(x^2+z^2)) and yaw = atan2(z, sqrt(x^2+y^2))

Why do these have to be done in the driver, rather than userland?

> Alternatively, just provide a data table, indexed by 0..255 x 0..255,
> with the second operand shifted and the sqrt computed in integer
> math.  Search wikipedia for easy algorithms to compute isqrt.

Since sqrt isn't being used in full generality, but just for hypot(),
you could use a lookup table for that too.  Even with cache miss
effects I suspect it may be faster than integer square root code
(though I'd want to benchmark before saying anything definite).

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