Swift extensions: Bit access for UInt8

Sometimes it is necessary to address the individual bits in a byte. This extension adds that capability to the UInt8 type:

extension UInt8 {

    

    static var bit7mask: UInt8 { return 0b1000_0000 }
    static var bit6mask: UInt8 { return 0b0100_0000 }
    static var bit5mask: UInt8 { return 0b0010_0000 }
    static var bit4mask: UInt8 { return 0b0001_0000 }
    static var bit3mask: UInt8 { return 0b0000_1000 }
    static var bit2mask: UInt8 { return 0b0000_0100 }
    static var bit1mask: UInt8 { return 0b0000_0010 }
    static var bit0mask: UInt8 { return 0b0000_0001 }

    

    func toBools() -> (bit7: Bool, bit6: Bool, bit5: Bool, bit4: Bool, bit3: Bool, bit2: Bool, bit1: Bool, bit0: Bool) {
        return (
            self & UInt8.bit7mask == UInt8.bit7mask,
            self & UInt8.bit6mask == UInt8.bit6mask,
            self & UInt8.bit5mask == UInt8.bit5mask,
            self & UInt8.bit4mask == UInt8.bit4mask,
            self & UInt8.bit3mask == UInt8.bit3mask,
            self & UInt8.bit2mask == UInt8.bit2mask,
            self & UInt8.bit1mask == UInt8.bit1mask,
            self & UInt8.bit0mask == UInt8.bit0mask
        )
    }

        

    func bit7IsSet() -> Bool { return self & UInt8.bit7mask == UInt8.bit7mask }
    func bit6IsSet() -> Bool { return self & UInt8.bit6mask == UInt8.bit6mask }
    func bit5IsSet() -> Bool { return self & UInt8.bit5mask == UInt8.bit5mask }
    func bit4IsSet() -> Bool { return self & UInt8.bit4mask == UInt8.bit4mask }
    func bit3IsSet() -> Bool { return self & UInt8.bit3mask == UInt8.bit3mask }
    func bit2IsSet() -> Bool { return self & UInt8.bit2mask == UInt8.bit2mask }
    func bit1IsSet() -> Bool { return self & UInt8.bit1mask == UInt8.bit1mask }
    func bit0IsSet() -> Bool { return self & UInt8.bit0mask == UInt8.bit0mask }

    

    func bit7IsNotSet() -> Bool { return self & UInt8.bit7mask == 0 }
    func bit6IsNotSet() -> Bool { return self & UInt8.bit6mask == 0 }
    func bit5IsNotSet() -> Bool { return self & UInt8.bit5mask == 0 }
    func bit4IsNotSet() -> Bool { return self & UInt8.bit4mask == 0 }
    func bit3IsNotSet() -> Bool { return self & UInt8.bit3mask == 0 }
    func bit2IsNotSet() -> Bool { return self & UInt8.bit2mask == 0 }
    func bit1IsNotSet() -> Bool { return self & UInt8.bit1mask == 0 }
    func bit0IsNotSet() -> Bool { return self & UInt8.bit0mask == 0 }

}

The toBools() function is intended to be used as follows:

struct ID3v2_3_HeaderFlags {

    let unsynchronisation: Bool

    let extendedHeader: Bool

    let experimental: Bool

    

    

    /// Returns nil if the byte does not contain valid header flags

    

    init?(byte: UInt8) {

        

        let b4, b3, b2, b1, b0: Bool // Unused, should be zero

        (unsynchronisation, extendedHeader, experimental, b4, b3, b2, b1, b0) = byte.toBools()

        if b4 || b3 || b2 || b1 || b0 { return nil }

    }

}

What I like about this is that the tuple return guarantees us that the compiler will check if all bools have an assigned variable.

Happy coding...

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