[libcamera-devel] [PATCH v5 2/9] android: metadata: Add hasEntry and entryContains

[Jacopo Mondi]

Hi LAurent,

On Sun, Jul 25, 2021 at 03:37:42AM +0300, Laurent Pinchart wrote:
> Hi Paul,
>
> Thank you for the patch.
>
> On Tue, Jul 20, 2021 at 07:13:00PM +0900, Paul Elder wrote:
> > Add convenience functions for checking if an entry is present in a
> > CameraMetadata instance, and to check if an array entry includes a
> > specific value.
> >
> > Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> >
> > ---
> > Changes in v5:
> > - refactor template code to reduce the footprint of specialized template
> >   code
> >
> > New in v4
> > ---
> >  src/android/camera_metadata.cpp | 18 ++++++++++++++++++
> >  src/android/camera_metadata.h   | 14 ++++++++++++++
> >  2 files changed, 32 insertions(+)
> >
> > diff --git a/src/android/camera_metadata.cpp b/src/android/camera_metadata.cpp
> > index 3fc7cf27..ac86c5fc 100644
> > --- a/src/android/camera_metadata.cpp
> > +++ b/src/android/camera_metadata.cpp
> > @@ -121,6 +121,24 @@ bool CameraMetadata::resize(size_t count, size_t size)
> >  	return true;
> >  }
> >
> > +template<>
> > +bool CameraMetadata::entryContainsOne<uint8_t>(const camera_metadata_ro_entry_t &entry,
> > +					       uint8_t value) const
> > +{
> > +	for (unsigned int i = 0; i < entry.count; i++) {
> > +		if (entry.data.u8[i] == value)
> > +			return true;
> > +	}
> > +
> > +	return false;
> > +}
>
> You'll get a linker error if you call entryContains() with a type
> different than uint8_t. Is there a use case for that ?
>

Why is this an issue ? As one needs more specialization they will be
added, otherwise should the function be specialized for all types even
if not used ? There are not many many types so that could be done
already, but I don't think it's strictly necessary.

> > +
> > +bool CameraMetadata::hasEntry(uint32_t tag) const
> > +{
> > +	camera_metadata_ro_entry_t entry;
> > +	return getEntry(tag, &entry);
> > +}
> > +
> >  bool CameraMetadata::addEntry(uint32_t tag, const void *data, size_t count,
> >  			      size_t elementSize)
> >  {
> > diff --git a/src/android/camera_metadata.h b/src/android/camera_metadata.h
> > index 3b7c9e24..72ba4db2 100644
> > --- a/src/android/camera_metadata.h
> > +++ b/src/android/camera_metadata.h
> > @@ -29,6 +29,20 @@ public:
> >  	bool isValid() const { return valid_; }
> >  	bool getEntry(uint32_t tag, camera_metadata_ro_entry_t *entry) const;
> >
> > +	template<typename T>
> > +	bool entryContainsOne(const camera_metadata_ro_entry_t &entry, T value) const;
>
> Unless you intend for this to be called directly, let's make it private.
>
> > +
> > +	template<typename T> bool entryContains(uint32_t tag, T value) const
> > +	{
> > +		camera_metadata_ro_entry_t entry;
> > +		if (!getEntry(tag, &entry))
> > +			return false;
> > +
> > +		return entryContainsOne<T>(entry, value);
> > +	}
>
> So the part you inline is the one that doesn't depend on the type T, and
> the part you don't inline is that one that does ? That seems a bit
> backwards, I'd move merge the two functions and move all the code to the
> .cpp file.
>

I suggested Paul to inline the common part and only specialize the
type-dependent part. That's why I was asking about the memory
footprint.

How would you do it backwards ?

Otherwise yes, merge all in the .cpp file but be aware that the
entryContains() function content will be replicated in each
specialization ?

> > +
> > +	bool hasEntry(uint32_t tag) const;
> > +
> >  	template<typename T,
> >  		 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
> >  	bool addEntry(uint32_t tag, const T &data)
>
> --
> Regards,
>
> Laurent Pinchart