find distance x0 is from segment x1-x2

Transforms even the sequence 0,1,2,3,... into reasonably good random numbers Challenge: improve on this in speed and "randomness"! This seems to pass

calculate twice signed area of triangle (0,0)-(x1,y1)-(x2,y2) return an SOS-determined sign (-1, +1, or 0 only if it's a truly degenerate triangle)

find distance x0 is from triangle x1-x2-x3

a useful core hash function

robust test of (x0,y0) in the triangle (x1,y1)-(x2,y2)-(x3,y3) if true is returned, the barycentric coordinates are set in a,b,c.