How to convert Data to hex string in swift - swift

I want the hexadecimal representation of a Data value in Swift.
Eventually I'd want to use it like this:
let data = Data(base64Encoded: "aGVsbG8gd29ybGQ=")!
print(data.hexString)

A simple implementation (taken from How to hash NSString with SHA1 in Swift?, with an additional option for uppercase output) would be
extension Data {
struct HexEncodingOptions: OptionSet {
let rawValue: Int
static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
}
func hexEncodedString(options: HexEncodingOptions = []) -> String {
let format = options.contains(.upperCase) ? "%02hhX" : "%02hhx"
return self.map { String(format: format, $0) }.joined()
}
}
I chose a hexEncodedString(options:) method in the style of the existing method base64EncodedString(options:).
Data conforms to the Collection protocol, therefore one can use
map() to map each byte to the corresponding hex string.
The %02x format prints the argument in base 16, filled up to two digits
with a leading zero if necessary. The hh modifier causes the argument
(which is passed as an integer on the stack) to be treated as a one byte
quantity. One could omit the modifier here because $0 is an unsigned
number (UInt8) and no sign-extension will occur, but it does no harm leaving
it in.
The result is then joined to a single string.
Example:
let data = Data([0, 1, 127, 128, 255])
// For Swift < 4.2 use:
// let data = Data(bytes: [0, 1, 127, 128, 255])
print(data.hexEncodedString()) // 00017f80ff
print(data.hexEncodedString(options: .upperCase)) // 00017F80FF
The following implementation is faster by a factor about 50
(tested with 1000 random bytes). It is inspired to
RenniePet's solution
and Nick Moore's solution, but takes advantage of
String(unsafeUninitializedCapacity:initializingUTF8With:)
which was introduced with Swift 5.3/Xcode 12 and is available on macOS 11 and iOS 14 or newer.
This method allows to create a Swift string from UTF-8 units efficiently, without unnecessary copying or reallocations.
An alternative implementation for older macOS/iOS versions is also provided.
extension Data {
struct HexEncodingOptions: OptionSet {
let rawValue: Int
static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
}
func hexEncodedString(options: HexEncodingOptions = []) -> String {
let hexDigits = options.contains(.upperCase) ? "0123456789ABCDEF" : "0123456789abcdef"
if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
let utf8Digits = Array(hexDigits.utf8)
return String(unsafeUninitializedCapacity: 2 * self.count) { (ptr) -> Int in
var p = ptr.baseAddress!
for byte in self {
p[0] = utf8Digits[Int(byte / 16)]
p[1] = utf8Digits[Int(byte % 16)]
p += 2
}
return 2 * self.count
}
} else {
let utf16Digits = Array(hexDigits.utf16)
var chars: [unichar] = []
chars.reserveCapacity(2 * self.count)
for byte in self {
chars.append(utf16Digits[Int(byte / 16)])
chars.append(utf16Digits[Int(byte % 16)])
}
return String(utf16CodeUnits: chars, count: chars.count)
}
}
}

This code extends the Data type with a computed property. It iterates through the bytes of data and concatenates the byte's hex representation to the result:
extension Data {
var hexDescription: String {
return reduce("") {$0 + String(format: "%02x", $1)}
}
}

My version. It's about 10 times faster than the [original] accepted answer by Martin R.
public extension Data {
private static let hexAlphabet = Array("0123456789abcdef".unicodeScalars)
func hexStringEncoded() -> String {
String(reduce(into: "".unicodeScalars) { result, value in
result.append(Self.hexAlphabet[Int(value / 0x10)])
result.append(Self.hexAlphabet[Int(value % 0x10)])
})
}
}

Swift 4 - From Data to Hex String
Based upon Martin R's solution but even a tiny bit faster.
extension Data {
/// A hexadecimal string representation of the bytes.
func hexEncodedString() -> String {
let hexDigits = Array("0123456789abcdef".utf16)
var hexChars = [UTF16.CodeUnit]()
hexChars.reserveCapacity(count * 2)
for byte in self {
let (index1, index2) = Int(byte).quotientAndRemainder(dividingBy: 16)
hexChars.append(hexDigits[index1])
hexChars.append(hexDigits[index2])
}
return String(utf16CodeUnits: hexChars, count: hexChars.count)
}
}
Swift 4 - From Hex String to Data
I've also added a fast solution for converting a hex String into Data (based on a C solution).
extension String {
/// A data representation of the hexadecimal bytes in this string.
func hexDecodedData() -> Data {
// Get the UTF8 characters of this string
let chars = Array(utf8)
// Keep the bytes in an UInt8 array and later convert it to Data
var bytes = [UInt8]()
bytes.reserveCapacity(count / 2)
// It is a lot faster to use a lookup map instead of strtoul
let map: [UInt8] = [
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, // 01234567
0x08, 0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 89:;<=>?
0x00, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x00, // #ABCDEFG
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 // HIJKLMNO
]
// Grab two characters at a time, map them and turn it into a byte
for i in stride(from: 0, to: count, by: 2) {
let index1 = Int(chars[i] & 0x1F ^ 0x10)
let index2 = Int(chars[i + 1] & 0x1F ^ 0x10)
bytes.append(map[index1] << 4 | map[index2])
}
return Data(bytes)
}
}
Note: this function does not validate the input. Make sure that it is only used for hexadecimal strings with (an even amount of) characters.

Backward compatible and fast solution:
extension Data {
/// Fast convert to hex by reserving memory (instead of mapping and join).
public func toHex(uppercase: Bool = false) -> String {
// Constants (Hex has 2 characters for each Byte).
let size = self.count * 2;
let degitToCharMap = Array((
uppercase ? "0123456789ABCDEF" : "0123456789abcdef"
).utf16);
// Reserve dynamic memory (plus one for null termination).
let buffer = UnsafeMutablePointer<unichar>.allocate(capacity: size + 1);
// Convert each byte.
var index = 0
for byte in self {
buffer[index] = degitToCharMap[Int(byte / 16)];
index += 1;
buffer[index] = degitToCharMap[Int(byte % 16)];
index += 1;
}
// Set Null termination.
buffer[index] = 0;
// Casts to string (without any copying).
return String(utf16CodeUnitsNoCopy: buffer,
count: size, freeWhenDone: true)
}
}
Note that above passes ownership of buffer to returned String object.
Also know that, because Swift's internal String data is UTF16 (but can be UTF8 since Swift 5), all solutions provided in accepted answer do full copy (and are slower), at least if NOT #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) ;-)
As mentioned on my profile, usage under Apache 2.0 license is allowed too (without attribution need).

This doesn't really answer the OP's question since it works on a Swift byte array, not a Data object. And it's much bigger than the other answers. But it should be more efficient since it avoids using String(format: ).
Anyway, in the hopes someone finds this useful ...
public class StringMisc {
// MARK: - Constants
// This is used by the byteArrayToHexString() method
private static let CHexLookup : [Character] =
[ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F" ]
// Mark: - Public methods
/// Method to convert a byte array into a string containing hex characters, without any
/// additional formatting.
public static func byteArrayToHexString(_ byteArray : [UInt8]) -> String {
var stringToReturn = ""
for oneByte in byteArray {
let asInt = Int(oneByte)
stringToReturn.append(StringMisc.CHexLookup[asInt >> 4])
stringToReturn.append(StringMisc.CHexLookup[asInt & 0x0f])
}
return stringToReturn
}
}
Test case:
// Test the byteArrayToHexString() method
let byteArray : [UInt8] = [ 0x25, 0x99, 0xf3 ]
assert(StringMisc.byteArrayToHexString(byteArray) == "2599F3")

A bit different from other answers here:
extension DataProtocol {
func hexEncodedString(uppercase: Bool = false) -> String {
return self.map {
if $0 < 16 {
return "0" + String($0, radix: 16, uppercase: uppercase)
} else {
return String($0, radix: 16, uppercase: uppercase)
}
}.joined()
}
}
However in my basic XCTest + measure setup this was fastest of the 4 I tried.
Going through a 1000 bytes of (the same) random data 100 times each:
Above: Time average: 0.028 seconds, relative standard deviation: 1.3%
MartinR: Time average: 0.037 seconds, relative standard deviation: 6.2%
Zyphrax: Time average: 0.032 seconds, relative standard deviation: 2.9%
NickMoore: Time average: 0.039 seconds, relative standard deviation: 2.0%
Repeating the test returned the same relative results. (Nick and Martins sometimes swapped)
Edit:
Nowadays I use this:
var hexEncodedString: String {
return self.reduce(into:"") { result, byte in
result.append(String(byte >> 4, radix: 16))
result.append(String(byte & 0x0f, radix: 16))
}
}

Maybe not the fastest, but data.map({ String($0, radix: 16) }).joined() does the job. As mentioned in the comments, this solution was flawed.

Related

UInt32 array to String Byte Array in Swift

Before I start I would like to apologise if I say something crazy.
I am working on an app that implements a c library. Among others, It shares idArrays.
I have the part decodes an idArray and it was given to me:
func decodeArrayID(aArray:UnsafeMutablePointer<CChar>, aTokenLen:UInt32)->([UInt32], String){
let arrayCount = Int(aTokenLen / 4)
var idArrayTemp = [UInt32]()
var idArrayStringTemp = ""
for i in 0..<arrayCount{
let idValue = decodeArrayIDItem(index: i, array: aArray)
idArrayTemp.append(idValue)
idArrayStringTemp += "\(idValue) "
}
return (idArrayTemp, idArrayStringTemp)
}
func decodeArrayIDItem(index:Int, array:UnsafeMutablePointer<CChar>) -> UInt32{
var value:UInt32 = UInt32(array[index * 4]) & 0xFF
value <<= 8
value |= UInt32(array [index * 4 + 1]) & 0xFF
value <<= 8
value |= UInt32(array [index * 4 + 2]) & 0xFF
value <<= 8
value |= UInt32(array [index * 4 + 3]) & 0xFF
return value
}
As we can see the idArray is send through UnsafeMutablePointer AKA UnsafeMutablePointer.
Now I am working with the encoding part. The function will take an array of UInt32 values and will try to convert it into byte array and will convert into a sting for sending it through the library.
So far I have the following code but it doesn't work:
func encodeIDArray(idArray:[UInt32])->String{
var aIDArray8:[UInt8] = [UInt8]()
for var value in idArray{
let count = MemoryLayout<UInt32>.size
let bytePtr = withUnsafePointer(to: &value) {
$0.withMemoryRebound(to: UInt8.self, capacity: count) {
UnsafeBufferPointer(start: $0, count: count)
}
}
aIDArray8 += Array(bytePtr)
}
let stringTest = String(data: Data(aIDArray8), encoding: .utf8)
return stringTest!
}
A test result for the input [1,2] returns "\u{01}\0\0\0\u{02}\0\0\0" and something tells is not quite right...
Thank you
Edited
The c functions are
DllExport void STDCALL DvProviderAvOpenhomeOrgPlaylist1EnableActionIdArray(THandle aProvider, CallbackPlaylist1IdArray aCallback, void* aPtr);
where CallbackPlaylist1IdArray is
typedef int32_t (STDCALL *CallbackPlaylist1IdArray)(void* aPtr, IDvInvocationC* aInvocation, void* aInvocationPtr, uint32_t* aToken, char** aArray, uint32_t* aArrayLen);
and the value to aArray is the value that get the Byte array
I believe you are in the right way
func encodeIDArray(idArray:[UInt32])->String{
var aIDArray8:[UInt8] = [UInt8]()
for var value in idArray{
let count = MemoryLayout<UInt32>.size
let bytePtr = withUnsafePointer(to: &value) {
$0.withMemoryRebound(to: UInt8.self, capacity: count) { v in
//Just change it to don't return the pointer itself, but the result of the rebound
UnsafeBufferPointer(start: v, count: count)
}
}
aIDArray8 += Array(bytePtr)
}
let stringTest = String(data: Data(aIDArray8), encoding: .utf8)
return stringTest!
}
Change your test to a some valid value in ASCII Table like this
encodeIDArray(idArray: [65, 66, 67]) // "ABC"
I hope it help you... Good luck and let me know it it works on your case.
You can copy the [UInt32] array values to the allocated memory without creating an intermediate [Int8] array, and use the bigEndian
property instead of bit shifting and masking:
func writeCArrayValue(from pointer:UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>?,
withUInt32Values array: [UInt32]){
pointer?.pointee = UnsafeMutablePointer<Int8>.allocate(capacity: MemoryLayout<UInt32>.size * array.count)
pointer?.pointee?.withMemoryRebound(to: UInt32.self, capacity: array.count) {
for i in 0..<array.count {
$0[i] = array[i].bigEndian
}
}
}
In the same way you can do the decoding:
func decodeArrayID(aArray:UnsafeMutablePointer<CChar>, aTokenLen:UInt32)->[UInt32] {
let arrayCount = Int(aTokenLen / 4)
var idArrayTemp = [UInt32]()
aArray.withMemoryRebound(to: UInt32.self, capacity: arrayCount) {
for i in 0..<arrayCount {
idArrayTemp.append(UInt32(bigEndian: $0[i]))
}
}
return idArrayTemp
}
You can't convert a binary buffer to a string and expect it to work. You should base64 encode your binary data. That IS a valid way to represent binary data as strings.
Consider the following code:
//Utility function that takes a typed pointer to a data buffer an converts it to an array of the desired type of object
func convert<T>(count: Int, data: UnsafePointer<T>) -> [T] {
let buffer = UnsafeBufferPointer(start: data, count: count);
return Array(buffer)
}
//Create an array of UInt32 values
let intArray: [UInt32] = Array<UInt32>(1...10)
print("source arrray = \(intArray)")
let arraySize = MemoryLayout<UInt32>.size * intArray.count
//Convert the array to a Data object
let data = Data(bytes: UnsafeRawPointer(intArray),
count: arraySize)
//Convert the binary Data to base64
let base64String = data.base64EncodedString()
print("Array as base64 data = ", base64String)
if let newData = Data(base64Encoded: base64String) {
newData.withUnsafeBytes { (bytes: UnsafePointer<UInt32>)->Void in
let newArray = convert(count:10, data: bytes)
print("After conversion, newArray = ", newArray)
}
} else {
fatalError("Failed to base-64 decode data!")
}
The output of that code is:
source arrray =[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Array as base64 data = AQAAAAIAAAADAAAABAAAAAUAAAAGAAAABwAAAAgAAAAJAAAACgAAAA==
After conversion, newArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Program ended with exit code: 0
Although I really appreciate all the answers I have finally figured out what was happening. I have to say that Duncan's answer was the closest to my problem.
So far I have interpreted char** as String. Turns out that it can be also a pointer to an array (Correct me if I am Wrong!). Converting the array as String gave a format that the library didn't like and it could not be decode on the other end.
The way I ended up doing is:
func encodeIDArray(idArray:[UInt32])->[Int8]{
var aIDArray8 = [UInt8].init(repeating: 0, count: idArray.count*4)
for i in 0..<idArray.count{
aIDArray8[i * 4] = UInt8(idArray[i] >> 24) & 0xff
aIDArray8[i * 4 + 1] = UInt8(idArray[i] >> 16) & 0xff
aIDArray8[i * 4 + 2] = UInt8(idArray[i] >> 8) & 0xff
aIDArray8[i * 4 + 3] = UInt8(idArray[i]) & 0xff
}
return aIDArray8.map { Int8(bitPattern: $0) }
}
and then I am assigning the value of the C Variable in swift like that:
let myArray = encodeIDArray(idArray:theArray)
writeCArrayValue(from: aArrayPointer, withValue: myArray)
func writeCArrayValue(from pointer:UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>?, withValue array:[Int8]){
pointer?.pointee = UnsafeMutablePointer<Int8>.allocate(capacity: array.count)
memcpy(pointer?.pointee, array, array.count)
}
aArrayPointer is a the char** used by the library.

How to convert my bytes data to Hex String and then Signed integer (32-bit) Two's complement from that ..?

I have a data like a bellow:
let data = Data(bytes: [206, 66, 49, 62])
Then I used this extension (from How to convert Data to hex string in swift) to convert to a hex string:
extension Data {
struct HexEncodingOptions: OptionSet {
let rawValue: Int
static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
}
func hexEncodedString(options: HexEncodingOptions = []) -> String {
let hexDigits = Array((options.contains(.upperCase) ? "0123456789ABCDEF" : "0123456789abcdef").utf16)
var chars: [unichar] = []
chars.reserveCapacity(2 * count)
for byte in self {
chars.append(hexDigits[Int(byte / 16)])
chars.append(hexDigits[Int(byte % 16)])
}
return String(utf16CodeUnits: chars, count: chars.count)
}
}
And then it is giving "ce42313e" as hex string. Now I am trying to convert this to Signed integer (32-bit) Two's complement .. I tried a couple of ways but not find anything perfectly.
When I give "ce42313e" in this bellow link under hex decimal the value is -834522818
http://www.binaryconvert.com/convert_signed_int.html
bellow is one of those I tried to convert "ce42313e" to int and it's giving me 3460444478 ..instead of -834522818 .
let str = value
let number = Int(str, radix: 16)
Please help out to get that value.
Int(str, radix: 16) interprets the string as the hexadecimal
representation of an unsigned number. You could convert it to
Int32 with
let data = Data(bytes: [206, 66, 49, 62])
let str = data.hexEncodedString()
print(str) // ce42313e
let number = Int32(truncatingBitPattern: Int(str, radix: 16)!)
print(number) // -834522818
But actually you don't need the hex representation for that purpose.
Your data is the big-endian representation of a signed 32-bit integer,
and this is how you can get the number from the data directly:
let data = Data(bytes: [206, 66, 49, 62])
let number = Int32(bigEndian: data.withUnsafeBytes { $0.pointee })
print(number) // -834522818

Convert Text String into Hex code [duplicate]

I want the hexadecimal representation of a Data value in Swift.
Eventually I'd want to use it like this:
let data = Data(base64Encoded: "aGVsbG8gd29ybGQ=")!
print(data.hexString)
A simple implementation (taken from How to hash NSString with SHA1 in Swift?, with an additional option for uppercase output) would be
extension Data {
struct HexEncodingOptions: OptionSet {
let rawValue: Int
static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
}
func hexEncodedString(options: HexEncodingOptions = []) -> String {
let format = options.contains(.upperCase) ? "%02hhX" : "%02hhx"
return self.map { String(format: format, $0) }.joined()
}
}
I chose a hexEncodedString(options:) method in the style of the existing method base64EncodedString(options:).
Data conforms to the Collection protocol, therefore one can use
map() to map each byte to the corresponding hex string.
The %02x format prints the argument in base 16, filled up to two digits
with a leading zero if necessary. The hh modifier causes the argument
(which is passed as an integer on the stack) to be treated as a one byte
quantity. One could omit the modifier here because $0 is an unsigned
number (UInt8) and no sign-extension will occur, but it does no harm leaving
it in.
The result is then joined to a single string.
Example:
let data = Data([0, 1, 127, 128, 255])
// For Swift < 4.2 use:
// let data = Data(bytes: [0, 1, 127, 128, 255])
print(data.hexEncodedString()) // 00017f80ff
print(data.hexEncodedString(options: .upperCase)) // 00017F80FF
The following implementation is faster by a factor about 50
(tested with 1000 random bytes). It is inspired to
RenniePet's solution
and Nick Moore's solution, but takes advantage of
String(unsafeUninitializedCapacity:initializingUTF8With:)
which was introduced with Swift 5.3/Xcode 12 and is available on macOS 11 and iOS 14 or newer.
This method allows to create a Swift string from UTF-8 units efficiently, without unnecessary copying or reallocations.
An alternative implementation for older macOS/iOS versions is also provided.
extension Data {
struct HexEncodingOptions: OptionSet {
let rawValue: Int
static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
}
func hexEncodedString(options: HexEncodingOptions = []) -> String {
let hexDigits = options.contains(.upperCase) ? "0123456789ABCDEF" : "0123456789abcdef"
if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) {
let utf8Digits = Array(hexDigits.utf8)
return String(unsafeUninitializedCapacity: 2 * self.count) { (ptr) -> Int in
var p = ptr.baseAddress!
for byte in self {
p[0] = utf8Digits[Int(byte / 16)]
p[1] = utf8Digits[Int(byte % 16)]
p += 2
}
return 2 * self.count
}
} else {
let utf16Digits = Array(hexDigits.utf16)
var chars: [unichar] = []
chars.reserveCapacity(2 * self.count)
for byte in self {
chars.append(utf16Digits[Int(byte / 16)])
chars.append(utf16Digits[Int(byte % 16)])
}
return String(utf16CodeUnits: chars, count: chars.count)
}
}
}
This code extends the Data type with a computed property. It iterates through the bytes of data and concatenates the byte's hex representation to the result:
extension Data {
var hexDescription: String {
return reduce("") {$0 + String(format: "%02x", $1)}
}
}
My version. It's about 10 times faster than the [original] accepted answer by Martin R.
public extension Data {
private static let hexAlphabet = Array("0123456789abcdef".unicodeScalars)
func hexStringEncoded() -> String {
String(reduce(into: "".unicodeScalars) { result, value in
result.append(Self.hexAlphabet[Int(value / 0x10)])
result.append(Self.hexAlphabet[Int(value % 0x10)])
})
}
}
Swift 4 - From Data to Hex String
Based upon Martin R's solution but even a tiny bit faster.
extension Data {
/// A hexadecimal string representation of the bytes.
func hexEncodedString() -> String {
let hexDigits = Array("0123456789abcdef".utf16)
var hexChars = [UTF16.CodeUnit]()
hexChars.reserveCapacity(count * 2)
for byte in self {
let (index1, index2) = Int(byte).quotientAndRemainder(dividingBy: 16)
hexChars.append(hexDigits[index1])
hexChars.append(hexDigits[index2])
}
return String(utf16CodeUnits: hexChars, count: hexChars.count)
}
}
Swift 4 - From Hex String to Data
I've also added a fast solution for converting a hex String into Data (based on a C solution).
extension String {
/// A data representation of the hexadecimal bytes in this string.
func hexDecodedData() -> Data {
// Get the UTF8 characters of this string
let chars = Array(utf8)
// Keep the bytes in an UInt8 array and later convert it to Data
var bytes = [UInt8]()
bytes.reserveCapacity(count / 2)
// It is a lot faster to use a lookup map instead of strtoul
let map: [UInt8] = [
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, // 01234567
0x08, 0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // 89:;<=>?
0x00, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x00, // #ABCDEFG
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 // HIJKLMNO
]
// Grab two characters at a time, map them and turn it into a byte
for i in stride(from: 0, to: count, by: 2) {
let index1 = Int(chars[i] & 0x1F ^ 0x10)
let index2 = Int(chars[i + 1] & 0x1F ^ 0x10)
bytes.append(map[index1] << 4 | map[index2])
}
return Data(bytes)
}
}
Note: this function does not validate the input. Make sure that it is only used for hexadecimal strings with (an even amount of) characters.
Backward compatible and fast solution:
extension Data {
/// Fast convert to hex by reserving memory (instead of mapping and join).
public func toHex(uppercase: Bool = false) -> String {
// Constants (Hex has 2 characters for each Byte).
let size = self.count * 2;
let degitToCharMap = Array((
uppercase ? "0123456789ABCDEF" : "0123456789abcdef"
).utf16);
// Reserve dynamic memory (plus one for null termination).
let buffer = UnsafeMutablePointer<unichar>.allocate(capacity: size + 1);
// Convert each byte.
var index = 0
for byte in self {
buffer[index] = degitToCharMap[Int(byte / 16)];
index += 1;
buffer[index] = degitToCharMap[Int(byte % 16)];
index += 1;
}
// Set Null termination.
buffer[index] = 0;
// Casts to string (without any copying).
return String(utf16CodeUnitsNoCopy: buffer,
count: size, freeWhenDone: true)
}
}
Note that above passes ownership of buffer to returned String object.
Also know that, because Swift's internal String data is UTF16 (but can be UTF8 since Swift 5), all solutions provided in accepted answer do full copy (and are slower), at least if NOT #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) ;-)
As mentioned on my profile, usage under Apache 2.0 license is allowed too (without attribution need).
This doesn't really answer the OP's question since it works on a Swift byte array, not a Data object. And it's much bigger than the other answers. But it should be more efficient since it avoids using String(format: ).
Anyway, in the hopes someone finds this useful ...
public class StringMisc {
// MARK: - Constants
// This is used by the byteArrayToHexString() method
private static let CHexLookup : [Character] =
[ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F" ]
// Mark: - Public methods
/// Method to convert a byte array into a string containing hex characters, without any
/// additional formatting.
public static func byteArrayToHexString(_ byteArray : [UInt8]) -> String {
var stringToReturn = ""
for oneByte in byteArray {
let asInt = Int(oneByte)
stringToReturn.append(StringMisc.CHexLookup[asInt >> 4])
stringToReturn.append(StringMisc.CHexLookup[asInt & 0x0f])
}
return stringToReturn
}
}
Test case:
// Test the byteArrayToHexString() method
let byteArray : [UInt8] = [ 0x25, 0x99, 0xf3 ]
assert(StringMisc.byteArrayToHexString(byteArray) == "2599F3")
A bit different from other answers here:
extension DataProtocol {
func hexEncodedString(uppercase: Bool = false) -> String {
return self.map {
if $0 < 16 {
return "0" + String($0, radix: 16, uppercase: uppercase)
} else {
return String($0, radix: 16, uppercase: uppercase)
}
}.joined()
}
}
However in my basic XCTest + measure setup this was fastest of the 4 I tried.
Going through a 1000 bytes of (the same) random data 100 times each:
Above: Time average: 0.028 seconds, relative standard deviation: 1.3%
MartinR: Time average: 0.037 seconds, relative standard deviation: 6.2%
Zyphrax: Time average: 0.032 seconds, relative standard deviation: 2.9%
NickMoore: Time average: 0.039 seconds, relative standard deviation: 2.0%
Repeating the test returned the same relative results. (Nick and Martins sometimes swapped)
Edit:
Nowadays I use this:
var hexEncodedString: String {
return self.reduce(into:"") { result, byte in
result.append(String(byte >> 4, radix: 16))
result.append(String(byte & 0x0f, radix: 16))
}
}
Maybe not the fastest, but data.map({ String($0, radix: 16) }).joined() does the job. As mentioned in the comments, this solution was flawed.

Swift NSData getBytes reversed

I made an app communicating with a device with Bluetooth Low Energy.
Basically, my app and this device have their own message syntax. They exchange data as bytes and each values in thoses data are reversed.
My problem is that after reversing back value, when I'm converting a 3 bytes value to an Int32, the NSData.getBytes function seems to reverse the value, so I have a wrong value. Example:
var value; // containing [ 0x01, 0xD3, 0x00 ]
value = value.reverse(); // Reverse back : [ 0x00, 0xD3, 0x01 ]
let numb = value.getUInt32(); // Numb will be 119552, instead of 54017...
I don't know if I'm clear enough on my problem, but here is my code. A function which reverse back data and then tries to convert data to int.
// Those functions are in an extension of NSData
func getRUInt32(range:NSRange) -> UInt32
{
var data = message.subdataWithRange(range); // Extract data from main message
data = data.reverse(); // Reverse back data
return data.getUInt32(); // Convert to UInt32
}
func getUInt32() -> UInt32
{
var value:Int32 = 0;
getBytes(&value, length: self.length);
return UInt32(value);
}
func reverse() -> NSData
{
let count:Int = length / sizeof(UInt8);
var array = [UInt8](count: count, repeatedValue: 0);
getBytes(&array, length: count * sizeof(UInt8));
var reversedArray = [UInt8](count: count, repeatedValue: 0);
for index in 0..<array.count
{
reversedArray[index] = array[array.count - index - 1];
}
return NSData(bytes: reversedArray, length: reversedArray.count);
}
You should have a look at the byte order utilities reference:
https://developer.apple.com/library/ios/documentation/CoreFoundation/Reference/CFByteOrderUtils/index.html#//apple_ref/c/func/CFConvertDoubleHostToSwapped
You identify the native format of the current platform using the
CFByteOrderGetCurrent function. Use functions such as
CFSwapInt32BigToHost and CFConvertFloat32HostToSwapped to convert
values between different byte order formats.

Binary to hexadecimal in Swift

I have a string in binary (for example "00100100"), and I want it in hexadecimal (like "24").
Is there a method written to convert Binary to Hexadecimal in Swift?
A possible solution:
func binToHex(bin : String) -> String {
// binary to integer:
let num = bin.withCString { strtoul($0, nil, 2) }
// integer to hex:
let hex = String(num, radix: 16, uppercase: true) // (or false)
return hex
}
This works as long as the numbers fit into the range of UInt (32-bit or 64-bit,
depending on the platform). It uses the BSD library function strtoul() which converts a string to an integer according to a given base.
For larger numbers you have to process the input
in chunks. You might also add a validation of the input string.
Update for Swift 3/4: The strtoul function is no longer needed.
Return nil for invalid input:
func binToHex(_ bin : String) -> String? {
// binary to integer:
guard let num = UInt64(bin, radix: 2) else { return nil }
// integer to hex:
let hex = String(num, radix: 16, uppercase: true) // (or false)
return hex
}
let binaryInteger = 0b1
// Your binary number
let hexadecimalNum = String(binaryInteger, radix: 16)
// convert into string format in whatever base you want
For more information
let decimalInteger = 15 // prefix NONE
let binaryInteger = 0b10001 // prefix 0b
let octalInteger = 0o21 // prefix 0o
let hexadecimalInteger = 0x11 // prefix 0x