CODEWITHSUNDEEP
swiftbluetooth-lowenergy
Mickael Belhassen
Mickael Belhassen

Reputation: 3352

Swift: hex number to Decimal from signed 2's complement Uint8

I have an array UInt8, I want to convert a hex number to decimal 2's complement:

var command = [UInt8]()
        command.append(0x24)
        command.append(0x17)
        command.append(UInt8(101))
        command.appendWithUint32Lsb(0)
        command.append(200)
        command.append(0)
        command.append(0xC8)
        command.append(0)
        command.append(0x20)
        command.append(3)
        command.append(7)
        command.append(0x00)
        command.append(UInt8(colors.count / 3))
        command.append(0xC8) <---- IR

According to this site https://www.rapidtables.com/convert/number/hex-to-decimal.html?x=0xC8

0xc8: Decimal number = 200

Decimal from signed 2's complement = -56

In my code when I print it:

[36, 23, 101, 0, 0, 0, 0, 200, 0, 200, 0, 32, 3, 7, 0, 3, 200]

But I do not want it to be 200 but -56

Here is the result I want:

[36, 23, 101, 0, 0, 0, 0, 200, 0, 200, 0, 32, 3, 7, 0, 3, -56]

How to do this?

Upvotes: 2

Views: 844

Answers (1)

Chris
Chris

Reputation: 3817

Your array is currently of type [UInt8] - it can't hold a value of -56.

Try this instead:

var command = [Int8]()
command.append(Int8(bitPattern: 0x24))
...
command.append(Int8(bitPattern: 0xc8))

Or transform what you already have:

let signedCommand = command.map { Int8(bitPattern: $0) }

Upvotes: 3

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