[SOLVED] How do you convert a UInt64 to an unsigned hex string in Swift?

How do you convert a UInt64 to an unsigned hex string in Swift?

Swift's String has String.init(_:radix:) initializer, which seems to let you convert Int values to hexadecimal. However, for values with the high bit set, it displays them as negative hex values.

How do you get a 64 bit integer to display in unsigned hexadecimal? String(format:) seems to only work on the low 32 bits of an Int.

This code:

let hashHex = String(hashValue, radix: 16, uppercase: true)

Creates strings like -5DB41312E0C8A0A9 (which presumably uses 2's compliment, and is not helpful.)

Solution

String.init(_:radix:uppercase:) works with any BinaryInteger. If the BinaryInteger is signed, then it will produce a signed string too.

hashValue is of type Int, which is signed. You can convert it to an UInt using init(bitPattern:). For example,

let hashValue = -1
print(String(UInt(bitPattern: hashValue), radix: 16))
// ffffffffffffffff

Note that it is incorrect to use UInt(hashValue) - the initialiser without any parameter labels will try to create a UInt with the numeric value, instead of preserving the bit pattern. UInt(-1) will crash because -1 is not a number representable by UInt.