[PATCH v2 02/17] libcamera: matrix: Make most functions constexpr

[Laurent Pinchart]

On Tue, Apr 01, 2025 at 03:59:57AM +0300, Laurent Pinchart wrote:
> Hi Stefan,
> 
> Thank you for the patch.
> 
> On Wed, Mar 19, 2025 at 05:11:07PM +0100, Stefan Klug wrote:
> > By zero-initializing the data_ member we can make most functions
> > constexpr which will come in handy in upcoming patches.  Note that this
> > is due to C++17. In C++20 we will be able to leave data_ unintialized
> 
> s/unintialized/uninitialized/
> 
> Given that we only operate on small matrices I think this is acceptable.
> Please add a todo comment to indicate that initialization of data should
> be removed with C++20.
> 
> > for constexpr.  The Matrix(std::array) version of the constructor can
> > not be constexpr because std::copy only became constexpr in C++20.

Actually, would open-coding std::copy allow making the constructor
constexpr ? If subsequent patches should be updated accordingly.

> > Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> > 
> > ---
> > 
> > Changes in v2:
> > - Added this patch
> > ---
> >  include/libcamera/internal/matrix.h | 15 +++++++--------
> >  1 file changed, 7 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/libcamera/internal/matrix.h b/include/libcamera/internal/matrix.h
> > index 8399be583f28..2e7929e9060c 100644
> > --- a/include/libcamera/internal/matrix.h
> > +++ b/include/libcamera/internal/matrix.h
> > @@ -25,9 +25,8 @@ class Matrix
> >  	static_assert(std::is_arithmetic_v<T>, "Matrix type must be arithmetic");
> >  
> >  public:
> > -	Matrix()
> > +	constexpr Matrix()
> >  	{
> > -		data_.fill(static_cast<T>(0));
> >  	}
> >  
> >  	Matrix(const std::array<T, Rows * Cols> &data)
> > @@ -35,7 +34,7 @@ public:
> >  		std::copy(data.begin(), data.end(), data_.begin());
> >  	}
> >  
> > -	static Matrix identity()
> > +	static constexpr Matrix identity()
> >  	{
> >  		Matrix ret;
> >  		for (size_t i = 0; i < std::min(Rows, Cols); i++)
> > @@ -63,14 +62,14 @@ public:
> >  		return out.str();
> >  	}
> >  
> > -	Span<const T, Rows * Cols> data() const { return data_; }
> > +	constexpr Span<const T, Rows * Cols> data() const { return data_; }
> >  
> > -	Span<const T, Cols> operator[](size_t i) const
> > +	constexpr Span<const T, Cols> operator[](size_t i) const
> >  	{
> >  		return Span<const T, Cols>{ &data_.data()[i * Cols], Cols };
> >  	}
> >  
> > -	Span<T, Cols> operator[](size_t i)
> > +	constexpr Span<T, Cols> operator[](size_t i)
> >  	{
> >  		return Span<T, Cols>{ &data_.data()[i * Cols], Cols };
> >  	}
> > @@ -85,7 +84,7 @@ public:
> >  	}
> >  
> >  private:
> > -	std::array<T, Rows * Cols> data_;
> > +	std::array<T, Rows * Cols> data_{};
> 
> We usually write
> 
> 	std::array<T, Rows * Cols> data_ = {};
> 
> With that and the comment,
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
> >  };
> >  
> >  template<typename T, typename U, unsigned int Rows, unsigned int Cols>
> > @@ -130,7 +129,7 @@ constexpr Matrix<T, R1, C2> operator*(const Matrix<T, R1, C1> &m1, const Matrix<
> >  }
> >  
> >  template<typename T, unsigned int Rows, unsigned int Cols>
> > -Matrix<T, Rows, Cols> operator+(const Matrix<T, Rows, Cols> &m1, const Matrix<T, Rows, Cols> &m2)
> > +constexpr Matrix<T, Rows, Cols> operator+(const Matrix<T, Rows, Cols> &m1, const Matrix<T, Rows, Cols> &m2)
> >  {
> >  	Matrix<T, Rows, Cols> result;
> >  

-- 
Regards,

Laurent Pinchart