[PATCH v3 07/16] libcamera: matrix: Extend multiplication operator to heterogenous types

[Stefan Klug]

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>
Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
Acked-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

---

Changes in v2:
- Added this patch

Changes in v3:
- Added my SoB tag
- Collected tags
---
 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 a07a47701336..47513b9950e4 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>
@@ -152,15 +153,16 @@ 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 68fc1b7bd5ac..ed22263b58f8 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