ParseHexString2.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ParseHex
{
    class Program
    {
        static void Main()
        {
            var bits = File.ReadAllBytes(@"SOME FILE HERE");
            var bitsLen = bits.Length;
            //	bitsLen = 2048;
            var str = BitConverter.ToString(bits, 0, bitsLen).Replace("-", "");
            var lines = BreakIntoLines(str, 512);
            var strrn = string.Join("\r\n", lines);

            Console.WriteLine($"str.len = {str.Length}");
            Console.WriteLine($"strrn.length = {strrn.Length}");

            var sw = new Stopwatch();
            sw.Start();
            var bits2 = ParseHexString(strrn);
            sw.Stop();

            Console.WriteLine($"Time: {sw.ElapsedMilliseconds}ms");

            if (bits.Length != bits2.Length)
            {
                Console.WriteLine($"{bitsLen} != {bits2.Length}");
                return;
            }

            for (var i1 = 0; i1 < bits.Length; i1++)
            {
                if (bits[i1] != bits2.Bits[i1])
                {
                    Console.WriteLine($"Bytes differ at {i1}: orig {bits[i1]:X2} new: {bits2.Bits[i1]:X2}");
                }
            }
        }

        private static (byte[] Bits, int Length) ParseHexString(string hex)
        {
            var destLength = hex.Length / 2;

            var source = hex.ToCharArray();
            var dest = new byte[destLength];

            //	int srcIndex = 0;

            int Nibble(int c)
            {
                if (c >= 'A')
                {
                    return (c - 'A') + 10;
                }

                return c - '0';
            }

            var dstIndex = 0;
            for (var srcIndex = 0; srcIndex < hex.Length; srcIndex++)
            {
                var nb = source[srcIndex++];
                if (nb == '\r' || nb == '\n')
                {
                    continue;
                }

                var b = Nibble(nb) << 4 | Nibble(source[srcIndex]);
                dest[dstIndex++] = (byte) b;
            }

            return (dest, dstIndex);
        }

        private static List<string> BreakIntoLines(string text, int width)
        {
            if (text == null)
            {
                throw new ArgumentNullException(nameof(text));
            }
            if (width < 1)
            {
                throw new ArgumentOutOfRangeException(nameof(width));
            }

            var pos = 0;
            var eol = text.Length;
            var lines = new List<string>();

            do
            {
                var len = eol - pos;
                len = Math.Min(len, width);
                var line = text.Substring(pos, len);
                lines.Add(line);

                pos += len;
            } while (eol > pos);

            return lines;
        }

    }
}