Galaxy-brain exactly(sign:magnitude:)

[oscbyspro]

While this API is still internal-ish, I'd like to note that formTwosComplementSubsequence(true) can replace the isZero check in exactly(sign:magnitude:). It's similar to (#6), hence the meme.

@inlinable public static func exactly<T>(sign: Sign, magnitude: T.Magnitude) -> T? where T: NBKFixedWidthInteger {
    var bitPattern = magnitude as T.Magnitude
    var isLessThanZero = (sign == Sign.minus)
    if  isLessThanZero {
        isLessThanZero = !bitPattern.formTwosComplementSubsequence(true)
    }
    
    let value = T(bitPattern: bitPattern)
    return value.isLessThanZero == isLessThanZero ? value : nil
}

[oscbyspro]

I had to check if minus zero fall under the definition of "exactly representable" and it does according to Swift:

let zero = Int(exactly: Double(sign: .minus, exponentBitPattern: 0, significandBitPattern: 0))