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I only learn of FloatingPointSign reading Tiny pitch: FloatingPointSign.negate(). I have no idea what's it used for.

Isn't all you need are x > 0 or x < 0?

Can anyone please give me one or two example of whatt this enum is used for?

@Nevin ?

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It’s the return type of the FloatingPoint.sign method, and is also used in the manual construction of new floating point values, as a parameter to FloatingPoint.init(sign:exponent:significand:).

I’m sure there are edge cases that come up that the sign method handles properly, where naive comparison against 0 would give an incorrect result. One that comes to mind is -Float.nan, which is neither less than, equal, nor greater than 0.

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It basically binds the required IEEE 754 isSignMinus operation, which is supposed to give you a way to extract the signbit that works for zeros and NaNs, where ‘x < 0’ would not.

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Given a chance to do it over, would you have preferred FloatingPoint.isSignMinus instead of FloatingPoint.sign?

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isNegative, no?

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isNegative can be misleading since the sign can be negative even if the value is zero (-0.0) or you are working with a NaN.

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I personally don't see a reason why FloatingPoint.isSignMinus would be a better name than FloatingPoint.sign. Plenty of Swift's FloatingPoint APIs use different names than the IEEE 754 standard. For example, instead of minNumMag(_:_:), Swift uses FloatingPoint.minimumMagnitude(_:_:), which is much clearer in my opinion. Instead of roundToIntegralTowardPositive(_:), Swift uses value.rounded(.up), which is also clearer.

value.sign == .plus is similarly much clearer than !value.isSignMinus.

This could cause subtle bugs. From the docs:

Don’t use this property to check whether a floating point value is negative. For a value x, the comparison x.sign == .minus is not necessarily the same as x < 0. In particular, x.sign == .minus if x is -0, and while x < 0 is always false if x is NaN, x.sign could be either .plus or .minus.

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