Swift Bitshift Integers in Array to the Right

Question

I've found a similar example in Python.

Essentially, say you have an array which is [1, 2, 3], and in binary that would be [0b00000001, 0b00000010, 0b00000011], what's the fastest way to bitshift that into [0b00000000, 0b10000001, 0b00000001]?

Basically bitshifting an array as if it were one huge int. (The left-hand side can always be assumed to be 0.)

Unfortunately I haven't got any code, because I have no clue how to achieve this, sorry!

Answer 1

I think you could do it something like this:

func bitShift(array: [UInt8]) -> [UInt8] {
  var output = array

  var prevParity = false

  for i in 0..<output.count {
    // check parity of current value and store it
    let tempParity = (output[i] & 1) == 1

    // bitshift the current value to the right
    output[i] = output[i] >> 1

    if prevParity {
      // add on the first one if the previous value was odd
      output[i] = output[i] | 0b10000000
    }

    // store tempParity into prevParity for next loop
    prevParity = tempParity
  }

  return output
}

Advanced operators... https://docs.swift.org/swift-book/LanguageGuide/AdvancedOperators.html