ShiftBud bit shift algorithm.

TuringMachine.swift

//
//  TuringMachine.swift
//  TuringBud
//
//  Created by Cem Olcay on 3/8/22.
//

import Foundation

class TuringMachine {
    var value: UInt16 = 0
    var currentStep: UInt16 = 0
    var length: UInt16 = 16

    init() {
        value = UInt16.random(in: UInt16.min..<UInt16.max)
    }

    func advance(bias: Double) {
        // Rotate the bit value
        value = shiftBitRight(value)

        if bias >= 0.5 {
            // Randomisation chance increases if the knob is near noon.
            // No randomisation chance if knob is fully rotated to right aka loop the 'length amount' steps.
            if Double.random(in: 0.5 ... 1.0) > bias {
                let random = randomBit()
                value = setBit(value, at: 15, to: random)
            }
        } else {
            // Flip chance increases if knob is near noon.
            // Always filp if the knob is fully rotated to the left aka loop twice the 'length amount' steps.
            if Double.random(in: 0.0 ... 0.5) >= bias {
                value = toggleBit(value, at: 15)
            }
        }

        currentStep += 1
        if currentStep >= length {
            currentStep = 0
            if bias == 0 || bias == 1 {
                var push = value
                for _ in 0..<length {
                    push = shiftBitLeft(push)
                }
                value = push
            }
        }
    }

    func randomBit() -> UInt16 {
        return Bool.random() ? 1 : 0
    }

    func setBit(_ i: UInt16, at n: UInt16, to k: UInt16) -> UInt16 {
        if k > 0 {
            return i | ( 1 << n)
        }
        return i & ~(1 << n)
    }

    func toggleBit(_ i: UInt16, at n: UInt16) -> UInt16 {
        return i ^ (1 << n)
    }

    func getBit(_ i: UInt16, at n: UInt16) -> UInt16 {
        return ((i >> n) & 1) == 1 ? 1 : 0
    }

    func shiftBitRight(_ i: UInt16) -> UInt16 {
        let lastBit = getBit(i, at: 0)
        let shift = (i >> 1)
        return setBit(shift, at: 15, to: lastBit)
    }

    func shiftBitLeft(_ i: UInt16) -> UInt16 {
        let firstBit = getBit(i, at: 15)
        let shift = (i << 1)
        return setBit(shift, at: 0, to: firstBit)
    }

    func printBit(_ i: UInt16) {
        let s = String(i, radix: 2)
        let p = (s.count..<16).map({ _ in "0" }).joined()
        print("\(i)\t\(p + s)")
    }
}