On 08/01/2014 06:19 PM, Antonio Ospite wrote:
On Fri, 01 Aug 2014 12:14:15 +0200
Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
On 07/31/2014 09:16 PM, Andy Walls wrote:
On Wed, 2014-07-30 at 16:23 +0200, Hans Verkuil wrote:
From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
[..]
+- Improve the sinus generation of the SDR radio.
Maybe a lookup table, containing the first quarter wave of cos() from 0
to pi/2 in pi/200 steps, and then linear interpolation for cos() of
angles in between those steps. You could go with a larger lookup table
with finer grained steps to reduce the approximation errors. A lookup
table with linear interpolation, I would think, requires fewer
mutliplies and divides than the current Taylor expansion computation.
Yeah, I had plans for that. There actually is a sine-table already in vivid-tpg.c
since I'm using that to implement Hue support.
I don't know what your requirements are here but JFTR there is already a
simplistic implementation of fixed point operations in
include/linux/fixp-arith.h I used them in
drivers/media/usb/gspca/ov534.c for some hue calculation.
I looked that too, but there was very small LUT => very bad resolution.
So I ended up copying sin/cos from cx88 driver (Taylor method).
regards
Antti
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