I have a string of binary values e.g. "010010000110010101111001". Is there a simple way to convert this string into its ascii representation to get (in this case) "Hey"?
Only found the other way or things for Integer:
let binary = "11001"
if let number = Int(binary, radix: 2) {
print(number) // Output: 25
}
Do someone know a good and efficient solution for this case?
A variant of @OOPer's solution would be to use a conditionally binding while loop and index(_:offsetBy:limitedBy:) in order to iterate over the 8 character substrings, taking advantage of the fact that index(_:offsetBy:limitedBy:) returns nil when you try to advance past the limit.
let binaryBits = "010010000110010101111001"
var result = ""
var index = binaryBits.startIndex
while let next = binaryBits.index(index, offsetBy: 8, limitedBy: binaryBits.endIndex) {
let asciiCode = UInt8(binaryBits[index..<next], radix: 2)!
result.append(Character(UnicodeScalar(asciiCode)))
index = next
}
print(result) // Hey
Note that we're going via Character rather than String in the intermediate step – this is simply to take advantage of the fact that Character is specially optimised for cases where the UTF-8 representation fits into 63 bytes, which is the case here. This saves heap-allocating an intermediate buffer for each character.
Purely for the fun of it, another approach could be to use sequence(state:next:) in order to create a sequence of the start and end indices of each substring, and then reduce in order to concatenate the resultant characters together into a string:
let binaryBits = "010010000110010101111001"
// returns a lazily evaluated sequence of the start and end indices for each substring
// of 8 characters.
let indices = sequence(state: binaryBits.startIndex, next: {
index -> (index: String.Index, nextIndex: String.Index)? in
let previousIndex = index
// Advance the current index – if it didn't go past the limit, then return the
// current index along with the advanced index as a new element of the sequence.
return binaryBits.characters.formIndex(&index, offsetBy: 8, limitedBy: binaryBits.endIndex) ? (previousIndex, index) : nil
})
// iterate over the indices, concatenating the resultant characters together.
let result = indices.reduce("") {
$0 + String(UnicodeScalar(UInt8(binaryBits[$1.index..<$1.nextIndex], radix: 2)!))
}
print(result) // Hey
On the face of it, this appears to be much less efficient than the first solution (due to the fact that reduce should copy the string at each iteration) – however it appears the compiler is able to perform some optimisations to make it not much slower than the first solution.
sequence(state:next), even though it usually tend to suffer w.r.t. performance when compared to more "classic" approaches. Incidentally, my vote (or a yet-to-be-updated shortly previous one) on this good answer should push you over 999 Swift tag upvotes. So grats somewhat in advance on the gold badge! :D
You may need to split the input binary digits into 8-bit chunks, and then convert each chunk to an ASCII character. I cannot think of a super simple way:
var binaryBits = "010010000110010101111001"
var index = binaryBits.startIndex
var result: String = ""
for _ in 0..<binaryBits.characters.count/8 {
let nextIndex = binaryBits.index(index, offsetBy: 8)
let charBits = binaryBits[index..<nextIndex]
result += String(UnicodeScalar(UInt8(charBits, radix: 2)!))
index = nextIndex
}
print(result) //->Hey
Does basically the same as OOPer's solution, but he/she was faster and has a shorter, more elegant approach :-)
func getASCIIString(from binaryString: String) -> String? {
guard binaryString.characters.count % 8 == 0 else {
return nil
}
var asciiCharacters = [String]()
var asciiString = ""
let startIndex = binaryString.startIndex
var currentLowerIndex = startIndex
while currentLowerIndex < binaryString.endIndex {
let currentUpperIndex = binaryString.index(currentLowerIndex, offsetBy: 8)
let character = binaryString.substring(with: Range(uncheckedBounds: (lower: currentLowerIndex, upper: currentUpperIndex)))
asciiCharacters.append(character)
currentLowerIndex = currentUpperIndex
}
for asciiChar in asciiCharacters {
if let number = UInt8(asciiChar, radix: 2) {
let character = String(describing: UnicodeScalar(number))
asciiString.append(character)
} else {
return nil
}
}
return asciiString
}
let binaryString = "010010000110010101111001"
if let asciiString = getASCIIString(from: binaryString) {
print(asciiString) // Hey
}
A different approach
let bytes_string: String = "010010000110010101111001"
var range_count: Int = 0
let characters_array: [String] = Array(bytes_string.characters).map({ String($0)})
var conversion: String = ""
repeat
{
let sub_range = characters_array[range_count ..< (range_count + 8)]
let sub_string: String = sub_range.reduce("") { $0 + $1 }
let character: String = String(UnicodeScalar(UInt8(sub_string, radix: 2)!))
conversion += character
range_count += 8
} while range_count < characters_array.count
print(conversion)
You can do this:
extension String {
var binaryToAscii: String {
stride(from: 0, through: count - 1, by: 8)
.map { i in map { String($0)}[i..<(i + 8)].joined() }
.map { String(UnicodeScalar(UInt8($0, radix: 2)!)) }
.joined()
}
}
