def Sqr_Chord_Len_C3V(vec1, vec2):
    """Computes the square length of the difference between the two arguments.
    The arguments are assumed to be 3d vectors (indexable items of length 3)."""
    diff0 = vec1[0] - vec2[0];
    diff1 = vec1[1] - vec2[1];
    diff2 = vec1[2] - vec2[2];

    result = diff0 * diff0 + diff1 * diff1 + diff2 * diff2;
    return result