Node.js to c# converting

Question

I have this function is Node.js

// @param {BigInteger} checksum
// @returns {Uint8Array}

function checksumToUintArray(checksum) {
  var result = new Uint8Array(8);
  for (var i = 0; i < 8; ++i) {
    result[7 - i] = checksum.and(31).toJSNumber();
    checksum = checksum.shiftRight(5);
  }
  return result;
}

What would be the equivalent in c#?

I'm thinking:

    public static uint[] ChecksumToUintArray(long checksum)
    {
        var result = new uint[8];
        for (var i = 0; i < 8; ++i)
        {
            result[7 - i] = (uint)(checksum & 31);
            checksum = checksum >> 5;         
        }
        return result;
    }

But I'm no sure. My main dilemma is the "BigInteger" type (but not only). Any help would be appropriated.

You should at least return uint[] or rename the method.

C.Evenhuis
– C.Evenhuis

2018-03-30 11:15:11 +00:00
Commented Mar 30, 2018 at 11:15 — C.Evenhuis
– C.Evenhuis, Commented Mar 30, 2018 at 11:15
@C.Evenhuis, Yes you are correct, I missed that.

zig
– zig

2018-03-30 11:30:27 +00:00
Commented Mar 30, 2018 at 11:30 — zig
– zig, Commented Mar 30, 2018 at 11:30

Evk · Accepted Answer · 2018-03-30 12:13:03Z

2

UInt8 is "unsigned 8-bit integer". In C# that's byte, because uint is "unsigned 32-bit integer". So UInt8Array is byte[].

Javascript BigInteger corresponds to C# BigInteger (from System.Numerics dll or nuget package), not to long. In some cases, long might be enough. For example, if BigInteger in javascript algorithm is used only because there is no such thing as 64bit integer in javascript - then it's fine to replace it with long in C#. But in general, without any additional information about expected ranges - range of javascript BigInteger is much bigger than range of C# long.

Knowing that, your method becomes:

public static byte[] ChecksumToUintArray(BigInteger checksum) {
    var result = new byte[8];
    for (var i = 0; i < 8; ++i) {
        result[7 - i] = (byte) (checksum & 31);
        checksum = checksum >> 5;
    }
    return result;
}

edited Mar 30, 2018 at 12:13

answered Mar 30, 2018 at 12:00

Evk

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2 Comments

zig Over a year ago

Thanks. is the js BigInteger signed?

Evk Over a year ago

There are several implementations of big integer in javascript. Mist popular has constructor argument as I remember, with which you can control whether it is signed or not.

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