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Probably shouldn’t include –0, which is used to represent underflow of negative numbers.

Why 3 more? Grandparent already counted one of the border points, so the correct number is either 1 more or 2 more, depending on whether you consider the floating point number -0 to be in the closed interval [0,1] or not.

See my other posting for more details: https://news.ycombinator.com/item?id=13772578

-0 is "below zero, but for so little that we cannot represent", so it's outside [0, 1].

Though for the purposes of comparisons, -0 and +0 are the same in IEEE 754.

So the expression "x >= 0.0f && x <= 1.0f" is true for x = -0.