Quaternion to 3x3 row major matrix

//-----------------------------------------------------------------------
void quaternion::toMatrix(mat3 &mat) const
{
    float x2 = x + x;
    float y2 = y + y;
    float z2 = z + z;

    float wx = x2 * w;
    float wy = y2 * w;
    float wz = z2 * w;
    float xx = x2 * x;
    float xy = y2 * x;
    float xz = z2 * x;
    float yy = y2 * y;
    float yz = z2 * y;
    float zz = z2 * z;

    mat[0] = 1.0f - (yy + zz); mat[1] = xy - wz; mat[2] = xz + wy;
    mat[3] = xy + wz; mat[4] = 1.0f - (xx + zz); mat[5] = yz - wx;
    mat[6] = xz - wy; mat[7] = yz + wx; mat[8] = 1.0f - (xx + yy);
}