Function orient2d 

pub fn orient2d(a: DVec2, b: DVec2, c: DVec2) -> Certified

Orientation of c relative to the directed line a -> b.

Returns Sign::Positive when a, b, c turn counter-clockwise, Sign::Negative for clockwise, and Sign::Zero when the three points are exactly collinear.

The result is Certified::Certain for every finite input: this function escalates to exact arithmetic internally, so it never returns an unproven sign. A caller may therefore use it to drive a topology decision directly. A non-finite coordinate returns Certified::Uncertain, not a guess.