Nice work! A little trick you can use here is squared distance which avoids the relatively expensive square root (also do the square in-place rather than pow)

Nice work! A little trick you can use here is squared distance which avoids the relatively expensive square root (also do the square in-place rather than pow) so your distance function becomes: (d - a) * (d - a) + (e - b) * (e - b) + (f - c) * (f - c) You will need to also square your threshold values.