System.Numerics.BigNumber.FormatBigIntegerToHexString C# (CSharp) Method

        private static string FormatBigIntegerToHexString(BigInteger value, char format, int digits, NumberFormatInfo info)
        {
            StringBuilder sb = new StringBuilder();
            byte[] bits = value.ToByteArray();
            string fmt = null;
            int cur = bits.Length - 1;

            if (cur > -1)
            {
                // [FF..F8] drop the high F as the two's complement negative number remains clear
                // [F7..08] retain the high bits as the two's complement number is wrong without it
                // [07..00] drop the high 0 as the two's complement positive number remains clear
                bool clearHighF = false;
                byte head = bits[cur];
                if (head > 0xF7)
                {
                    head -= 0xF0;
                    clearHighF = true;
                }
                if (head < 0x08 || clearHighF)
                {
                    // {0xF8-0xFF} print as {8-F}
                    // {0x00-0x07} print as {0-7}
                    fmt = string.Format(CultureInfo.InvariantCulture, "{0}1", format);
                    sb.Append(head.ToString(fmt, info));
                    cur--;
                }
            }
            if (cur > -1)
            {
                fmt = string.Format(CultureInfo.InvariantCulture, "{0}2", format);
                while (cur > -1)
                {
                    sb.Append(bits[cur--].ToString(fmt, info));
                }
            }
            if (digits > 0 && digits > sb.Length)
            {
                // Insert leading zeros.  User specified "X5" so we create "0ABCD" instead of "ABCD"
                sb.Insert(0, (value._sign >= 0 ? ("0") : (format == 'x' ? "f" : "F")), digits - sb.Length);
            }
            return sb.ToString();
        }