Question

How to set specific bits and find the set bits indexes in Swift

Answer 1

import Foundation

let bitSize = 16

// Print binary representation of the bits
func printBinary(_ bits: UInt16) {
    let binary = String(bits, radix: 2).leftPadding(toLength: bitSize, withPad: "0")
    print(binary)
}

// Find the first set bit (least significant)
func findFirstSetBit(_ bits: UInt16) -> Int? {
    for i in 0..<bitSize {
        if (bits >> i) & 1 == 1 {
            return i
        }
    }
    return nil
}

func printSetBitIndexes(_ bits: UInt16) {
    let indexes = (0..<bitSize).filter { (bits >> $0) & 1 == 1 }
    print(indexes.map(String.init).joined(separator: " "))
}

// String padding extension
extension String {
    func leftPadding(toLength: Int, withPad character: Character) -> String {
        let padCount = toLength - self.count
        guard padCount > 0 else { return self }
        
        return String(repeating: character, count: padCount) + self
    }
}


var bits: UInt16 = 0
bits |= 1 << 3
bits |= 1 << 5
bits |= 1 << 11
bits |= 1 << 14

printBinary(bits)

if let first = findFirstSetBit(bits) {
    print("First set bit at index: \(first)")
} else {
    print("No bits are set.")
}

print("All the set bits indexes:")
printSetBitIndexes(bits)


/*
run:

0100100000101000
First set bit at index: 3
All the set bits indexes:
3 5 11 14

*/

 

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