lib: Improve normal range calculation precision.
lib: Improve normal range calculation precision.

Addressed a potential catastrophic cancellation when calculating the
component of the range vector perpendicular to the image plane by
changing a calculation of the form (x*x - y*y) to the equivalent form
(x-y)(x+y) where cancellation due to subtraction is benign.

ossama-othman/MaRC,ossama-othman/MaRC,ossama-othman/MaRC