types - How to convert a gi-normous integer (in string format) to hex format? (C#)

Question

Given a potentially huge integer value (in C# string format), I want to be able to generate its hex equivalent. Normal methods don't apply here as we are talking arbitrarily large numbers, 50 digits or more. The techniques I've seen which use a technique like this:

// Store integer 182
int decValue = 182;
// Convert integer 182 as a hex in a string variable
string hexValue = decValue.ToString("X");
// Convert the hex string back to the number
int decAgain = int.Parse(hexValue, System.Globalization.NumberStyles.HexNumber);

won't work because the integer to convert is too large.

For example I need to be able to convert a string like this:

843370923007003347112437570992242323

to its hex equivalent.

these don't work:

C# convert integer to hex and back again How to convert numbers between hexadecimal and decimal in C#?

Answer 1

Oh, that's easy:

        var s = "843370923007003347112437570992242323";
        var result = new List<byte>();
        result.Add( 0 );
        foreach ( char c in s )
        {
            int val = (int)( c - '0' );
            for ( int i = 0 ; i < result.Count ; i++ )
            {
                int digit = result[i] * 10 + val;
                result[i] = (byte)( digit & 0x0F );
                val = digit >> 4;
            }
            if ( val != 0 )
                result.Add( (byte)val );
        }

        var hex = "";
        foreach ( byte b in result )
            hex = "0123456789ABCDEF"[ b ] + hex;