Added cross-product to vector implementation

src/linalg/vec.h

@@ -14,5 +14,6 @@ struct Vec3 {  // TODO: Maybe make this into a class
     __host__ __device__ Vec3 operator*(double b) const { return Vec3(x * b, y * b, z * b); }
     __host__ __device__ Vec3 operator-() const { return Vec3(-x, -y, -z); }
     __host__ __device__ double dot(const Vec3& b) const { return x * b.x + y * b.y + z * b.z; }
+    __host__ __device__ Vec3 cross(const Vec3& b) const { return Vec3(y * b.z - z * b.y, z * b.x - x * b.z, x * b.y - y * b.x); }
     __host__ __device__ Vec3 normalize() const { double len = sqrt(x * x + y * y + z * z); return Vec3(x / len, y / len, z / len); }
 };