vecmath.cpp

#include <iostream>

using namespace std;

struct vec3d
{
    float data[3];

    vec3d() : data{0.0f} {}

    vec3d(float x, float y, float z) { data[0] = x; data[1] = y; data[2] = z;}

    void print()
    {
        std::cout << "[" << data[0] << "][" << data[1] << "]["<< data[2] << "]" <<std::endl;
    }
};

struct mat3d
{
    vec3d data[3];

    mat3d(const vec3d& row1, const vec3d& row2, const vec3d& row3)
    {
        data[0] = row1; data[1] = row2; data[2] = row3;
    }

    void print()
    {
        for (size_t i=0; i < sizeof(data)/sizeof(data[0]); ++i)
            data[i].print();
    }
};

static vec3d  mult_vec_mat(const vec3d& v, const mat3d& mat)
{
    vec3d result;
    for(int i=0; i < 3; ++i)
    {
        float tmp = 0;
        for (int j=0; j < 3; ++j)
        {
            tmp += mat.data[i].data[j] * v.data[j];
        }
        result.data[i] = tmp;
    }
    return  result;
}


int main()
{
    vec3d v (2, 1, 3);
    mat3d m (vec3d(1,2,3), vec3d(4,5,6), vec3d(7,8,9));

    auto result = mult_vec_mat(v, m);
    result.print();

    return 0;
}