[PATCH v2 07/17] libcamera: matrix: Extend multiplication operator to heterogenous types

[Kieran Bingham]

Quoting Stefan Klug (2025-03-19 16:11:12)
> From: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
> It is useful to multiply matrices of heterogneous types, for instance
> float and double. Extend the multiplication operator to support this,
> avoiding the need to convert one of the matrices. The type of the
> returned matrix is selected automatically to avoid loosing precision.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Posted by Stefan, so should probably have your SoB - (or at least RB tag
now :D)

But this sounds like something that will be helpful later in this
series...


Acked-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

> 
> ---
> 
> Changes in v2:
> - Added this patch
> ---
>  include/libcamera/internal/matrix.h | 10 ++++++----
>  src/libcamera/matrix.cpp            |  5 +++--
>  2 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/include/libcamera/internal/matrix.h b/include/libcamera/internal/matrix.h
> index 6e3c190286fe..688c6fd498f3 100644
> --- a/include/libcamera/internal/matrix.h
> +++ b/include/libcamera/internal/matrix.h
> @@ -8,6 +8,7 @@
>  
>  #include <algorithm>
>  #include <sstream>
> +#include <type_traits>
>  #include <vector>
>  
>  #include <libcamera/base/log.h>
> @@ -129,15 +130,16 @@ constexpr Matrix<U, Rows, Cols> operator*(const Matrix<U, Rows, Cols> &m, T d)
>         return d * m;
>  }
>  
> -template<typename T, unsigned int R1, unsigned int C1, unsigned int R2, unsigned int C2>
> -constexpr Matrix<T, R1, C2> operator*(const Matrix<T, R1, C1> &m1, const Matrix<T, R2, C2> &m2)
> +template<typename T1, unsigned int R1, unsigned int C1, typename T2, unsigned int R2, unsigned int C2>
> +constexpr Matrix<std::common_type_t<T1, T2>, R1, C2> operator*(const Matrix<T1, R1, C1> &m1,
> +                                                              const Matrix<T2, R2, C2> &m2)
>  {
>         static_assert(C1 == R2, "Matrix dimensions must match for multiplication");
> -       Matrix<T, R1, C2> result;
> +       Matrix<std::common_type_t<T1, T2>, R1, C2> result;
>  
>         for (unsigned int i = 0; i < R1; i++) {
>                 for (unsigned int j = 0; j < C2; j++) {
> -                       T sum = 0;
> +                       std::common_type_t<T1, T2> sum = 0;
>  
>                         for (unsigned int k = 0; k < C1; k++)
>                                 sum += m1[i][k] * m2[k][j];
> diff --git a/src/libcamera/matrix.cpp b/src/libcamera/matrix.cpp
> index 8590f8efeff3..f9117357dc7e 100644
> --- a/src/libcamera/matrix.cpp
> +++ b/src/libcamera/matrix.cpp
> @@ -138,11 +138,12 @@ LOG_DEFINE_CATEGORY(Matrix)
>   */
>  
>  /**
> - * \fn Matrix<T, R1, C2> operator*(const Matrix<T, R1, C1> &m1, const Matrix<T, R2, C2> &m2)
> + * \fn operator*(const Matrix<T1, R1, C1> &m1, const Matrix<T2, R2, C2> &m2)
>   * \brief Matrix multiplication
> - * \tparam T Type of numerical values in the matrices
> + * \tparam T1 Type of numerical values in the first matrix
>   * \tparam R1 Number of rows in the first matrix
>   * \tparam C1 Number of columns in the first matrix
> + * \tparam T2 Type of numerical values in the secont matrix
>   * \tparam R2 Number of rows in the second matrix
>   * \tparam C2 Number of columns in the second matrix
>   * \param m1 Multiplicand matrix
> -- 
> 2.43.0
>