(a+b)+c = 1.0   a+(b+c) = 0.0
1e20, -1e20, 1.0 -> 1.0 0.0
three random values in [0,1): 0.956034243106842 0.9478274583816528 0.05655136704444885 -> 1.9604130983352661 1.9604129791259766
2**24, 1, 1 -> 16777216.0 16777218.0
