ipa: libipa: vector: Add matrix-vector multiplication

Add an operation for multiplying a matrix with a vector.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/libipa/vector.cpp

@@ -123,6 +123,17 @@ namespace ipa {
  * \return The length of the vector
  */
 
+/**
+ * \fn Vector<T, Rows> operator*(const Matrix<T, Rows, Cols> &m, const Vector<T, Cols> &v)
+ * \brief Multiply a matrix by a vector
+ * \tparam T Numerical type of the contents of the matrix and vector
+ * \tparam Rows The number of rows in the matrix
+ * \tparam Cols The number of columns in the matrix (= rows in the vector)
+ * \param m The matrix
+ * \param v The vector
+ * \return Product of matrix \a m and vector \a v
+ */
+
 /**
  * \fn bool operator==(const Vector<T, Rows> &lhs, const Vector<T, Rows> &rhs)
  * \brief Compare vectors for equality

src/ipa/libipa/vector.h

@@ -16,6 +16,8 @@
 
 #include "libcamera/internal/yaml_parser.h"
 
+#include "matrix.h"
+
 namespace libcamera {
 
 LOG_DECLARE_CATEGORY(Vector)
@@ -140,6 +142,21 @@ private:
 	std::array<T, Rows> data_;
 };
 
+template<typename T, unsigned int Rows, unsigned int Cols>
+Vector<T, Rows> operator*(const Matrix<T, Rows, Cols> &m, const Vector<T, Cols> &v)
+{
+	Vector<T, Rows> result;
+
+	for (unsigned int i = 0; i < Rows; i++) {
+		T sum = 0;
+		for (unsigned int j = 0; j < Cols; j++)
+			sum += m[i][j] * v[j];
+		result[i] = sum;
+	}
+
+	return result;
+}
+
 template<typename T, unsigned int Rows>
 bool operator==(const Vector<T, Rows> &lhs, const Vector<T, Rows> &rhs)
 {