Swift - Turn Int to binary representations

问题

I receive an Int from my server which I’d like to explode in to an array of bit masks. So for example, if my server gives me the number 3, we get two values, a binary 1 and a binary 2.

How do I do this in Swift?

回答1:

I am not aware of any nice built-in way, but you could use this:

var i = 3
let a = 0..<8

var b = a.map { Int(i & (1 << $0)) }
// b = [1, 2, 0, 0, 0, 0, 0, 0]

回答2:

You could use:

let number = 3
//radix: 2 is binary, if you wanted hex you could do radix: 16
let str = String(number, radix: 2)
println(str)

prints "11"

let number = 79
//radix: 2 is binary, if you wanted hex you could do radix: 16
let str = String(number, radix: 16)
println(str)

prints "4f"

回答3:

Here is a straightforward implementation:

func intToMasks(var n: Int) -> [Int] {
    var masks = [Int]()
    var mask = 1
    while n > 0 {
        if n & mask > 0 {
            masks.append(mask)
            n -= mask
        }
        mask <<= 1
    }
    return masks
}

println(intToMasks(3))    // prints "[1,2]"
println(intToMasks(1000)) // prints "[8,32,64,128,256,512]"

回答4:

public extension UnsignedInteger {
  /// The digits that make up this number.
  /// - Parameter radix: The base the result will use.
  func digits(radix: Self = 10) -> [Self] {
    sequence(state: self) { quotient in
      guard quotient > 0
      else { return nil }

      let division = quotient.quotientAndRemainder(dividingBy: radix)
      quotient = division.quotient
      return division.remainder
    }
    .reversed()
  }
}

let digits = (6 as UInt).digits(radix: 0b10) // [1, 1, 0]
digits.reversed().enumerated().map { $1 << $0 } // [0, 2, 4]

Reverse the result too, if you need it.

来源：https://stackoverflow.com/questions/28400705/swift-turn-int-to-binary-representations

标签

swift

bitmask