[libcamera-devel] [PATCH 0/2] Improve BayerFormat class

[Laurent Pinchart]

Hi Sebastian,

On Mon, Dec 28, 2020 at 08:05:28AM +0100, Sebastian Fricke wrote:
> On 26.12.2020 00:06, Laurent Pinchart wrote:
> >On Wed, Dec 23, 2020 at 01:10:53PM +0100, Sebastian Fricke wrote:
> >> This patch series adds unit-tests and the `fromV4L2PixelFormat` method
> >> to the BayerFormat class.
> >>
> >> I also wanted to discuss one alternative that I played around with.
> >> We could maybe drop one of the two mapping tables and use the following
> >> logic to get the map key from a mapped value.
> >>
> >> ```
> >> #include <algorithm>
> >> ...
> >> BayerFormat BayerFormat::fromV4L2PixelFormat(V4L2PixelFormat v4l2Format) const
> >> {
> >>     auto it = std::find_if(
> >>         bayerToV4l2.begin(),
> >>         bayerToV4l2.end(),
> >>         [v4l2Format](const auto& i) { return i->second == v4l2Format; }
> >>     );
> >>     if (it != bayerToV4l2.end())
> >>         return it->first;
> >>
> >>     return BayerFormat();
> >> }
> >> ```
> >
> > This would certainly work. The question is whether we can to optimize
> > the memory consumption (dropping the second lookup table), or the
> > execution time (a lookup operation for a map has a O(log(n)) complexity,
> > compared to O(n) for the code above).
> 
> Which probably boils down to the question: 'How often do we expect to
> use this function?'.
> Can you recall from the current code bases if there are cases, where the
> constructor is used frequently in a row? I would suspect that the
> constructor/static function should be used quite seldomly.

I don't expect this to be used in any hot path.

> >> Sebastian Fricke (2):
> >>   libcamera: Add the fromV4L2PixelFormat method
> >>   test: Add unit tests for the BayerFormat class
> >>
> >>  include/libcamera/internal/bayer_format.h |   1 +
> >>  src/libcamera/bayer_format.cpp            |  14 ++
> >>  test/bayer_format.cpp                     | 154 ++++++++++++++++++++++
> >>  test/meson.build                          |   1 +
> >>  4 files changed, 170 insertions(+)
> >>  create mode 100644 test/bayer_format.cpp

-- 
Regards,

Laurent Pinchart