Hi. I Made extension for BigInt to Data and reverse.

[OleksiiShulzhenko]

extension BigInt {
    
    public func serialize() -> Data {
        var array = Array(BigUInt.init(self.magnitude).serialize())
        
        if array.count > 0 {
            if self.sign == BigInt.Sign.plus {
                if array[0] >= 128 {
                    array.insert(0, at: 0)
                }
            } else if self.sign == BigInt.Sign.minus {
                if array[0] <= 127 {
                    array.insert(255, at: 0)
                }
            }
        }
        
        return Data.init(bytes: array)
    }
    
    public init(_ data: Data) {
        var dataArray = Array(data)
        var sign: BigInt.Sign = BigInt.Sign.plus
        
        if dataArray.count > 0 {
            if dataArray[0] >= 128 {
                sign = BigInt.Sign.minus
                
                if dataArray.count > 1 {
                    if dataArray[0] == 255, dataArray.count > 1 {
                        dataArray.remove(at: 0)
                    } else {
                        dataArray[0] = UInt8(256 - Int(dataArray[0]))
                    }
                }
            }
        }
        
        let magnitude = BigUInt.init(Data.init(bytes: dataArray))
        
        self .init(sign: sign, magnitude: magnitude)
    }
}

[HaydenMcCabe]

I created a pull request with a slightly different implementation of this idea, which you can take a look at. It's PR #61.

[tgymnich]

merged HaydenMcCabe approach

[sanjaykmwt94222]

@OleksiiShulzhenko's approach is more correct if we see what android's function toByteArray gives I was struggling for two days because the solution of @HaydenMcCabe Gives wrong output.

Please replace the serialize method of this library with @OleksiiShulzhenko's solution

[tgymnich]

I'll look into it. Do you have some examples for wrong output?

[sanjaykmwt94222]

You yourself can compare by giving the same input to the android and iOS and you will get different results

[koraykoska]

@sanjaykmwt94222 Please give us an example of exact input, expected output and the output of this library. Otherwise we will not be able to validate your request.

…

On Fri, Oct 9, 2020 at 12:03 sanjay kumawat ***@***.***> wrote: You yourself can compare by giving the same input to the android and iOS and you will get different results — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#54 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACWUTTLS7NABULWEPIZPMP3SJ3NXJANCNFSM4GMCSSJQ> .

[koraykoska]

@sanjaykmwt94222 <https://github.com/sanjaykmwt94222>

…

On Fri, Oct 9, 2020 at 12:07 Koray Koska ***@***.***> wrote: @sanjay Please give us an example of exact input, expected output and the output of this library. Otherwise we will not be able to validate your request. On Fri, Oct 9, 2020 at 12:03 sanjay kumawat ***@***.***> wrote: > You yourself can compare by giving the same input to the android and iOS > and you will get different results > > — > You are receiving this because you are subscribed to this thread. > Reply to this email directly, view it on GitHub > <#54 (comment)>, > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/ACWUTTLS7NABULWEPIZPMP3SJ3NXJANCNFSM4GMCSSJQ> > . >

[tgymnich]

I think what @sanjaykmwt94222 wants to say is, that our implementation of serialize() uses a sign byte and an unsigned integer, when javas BigInteger uses 2s complement to serialize big integers and no sign byte.

In my opinion the output is not wrong and the documentation clearly states the fact, that we are using a sign byte.

[sanjaykmwt94222]

@tgymnich Okay in that case there should be a function which gives output in 2s complement format same as android's BigInteger class

[koraykoska]

Sure. You can always make a PR and implement an overload or change this function to optionally accept a format

…

On Mon, Oct 12, 2020 at 07:43 sanjay kumawat ***@***.***> wrote: @tgymnich <https://github.com/tgymnich> Okay in that case there should be a function which gives output in 2s complement format same as android's BigInteger class — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#54 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACWUTTLJYB5KZGK6LLEMFDLSKKJQHANCNFSM4GMCSSJQ> .