CODEWITHSUNDEEP
iosiphoneswift
John
John

Reputation: 2480

Signed Hex to Signed Int Swift

I've seen a lot of questions converting hex to int, but these are all of the unsigned-> unsigned variety. How could I convert signed hex to an Int?

eg. 

somefunc('0xfffff830')
= -2000

Upvotes: 3

Views: 1873

Answers (3)

Martin R
Martin R

Reputation: 539975

Your question implies that you are dealing with 32-bit signed integers (otherwise 0xfffff830 could not be considered as negative), so this would work:

let num = "0xfffff830"

let x = Int32(truncatingBitPattern: strtoul(num, nil, 16))
println(x) // -2000

strtoul() converts the hex string to an unsigned integer UInt, and Int32(truncatingBitPattern:) creates a (signed) 32-bit integer from the lowest 32 bits of the given argument.

Updated for Swift 4:

let num = "0xfffff830"
let x = Int32(bitPattern: UInt32(num.dropFirst(2), radix: 16) ?? 0)
print(x) // -2000

Upvotes: 7

vadian
vadian

Reputation: 285200

An approach

var hex = UInt32(0xfffff830)
let signedHex : Int
if hex > UInt32.max / 2 {
  signedHex = -Int(~hex + 1) // ~ is the Bitwise NOT Operator
} else {
  signedHex = Int(hex)
}

Upvotes: 1

MirekE
MirekE

Reputation: 11555

You could use conversion to unsigned and then convert the unsigned to signed.

let num = "0xfffff830"
var result: UInt32 = 0
let converter = NSScanner(string: num)
converter.scanHexInt(&result)

print(unsafeBitCast(result, Int32.self)) // prints -2000

Upvotes: 2

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