using System;

using System.Text;

using System.Linq;

using System.Buffers.Binary;

​

public class Program

{

    delegate int BytesComparer(ReadOnlySpan<byte> a, ReadOnlySpan<byte> b);

​

    static int BinarySearchRecord(byte[] array, int recordWidth, ReadOnlySpan<byte> value, BytesComparer comparer)

    {

        return BinarySearchRecord(array, 0, array.Length / recordWidth, recordWidth, value, comparer);

    }

​

    static int BinarySearchRecord(byte[] array, int startRecord, int count, int recordWidth, ReadOnlySpan<byte> value, BytesComparer comparer)

    {

        int lo = startRecord;

        int hi = startRecord + count - 1;

        while (lo <= hi)

        {

            int i = lo + ((hi - lo) >> 1);

            int order = comparer(new ReadOnlySpan<byte>(array, i * recordWidth, recordWidth), value);

​

            if (order == 0) return i;

            if (order < 0)

                lo = i + 1;

            else

                hi = i - 1;

        }

​

        return ~lo;

    }

    public static void Main()

    {

        var yourArray = Encoding.ASCII.GetBytes("ABLE  xxxxBAKER xxxxCARL  xxxxDELTA xxxxEDGAR xxxxGEORGExxxx");

        var valToFind = Encoding.ASCII.GetBytes("DELTA ").Concat(new byte[]{0x1, 0x2, 0x3, 0x4}).ToArray();

​

        var foundIndex = BinarySearchRecord(yourArray, valToFind.Length, new ReadOnlySpan<byte>(valToFind), (a, b) =>

            {

                var ret = BinaryPrimitives.ReverseEndianness(BitConverter.ToInt64(a) & 0x0000ffffffffffff)

                    .CompareTo(

                          BinaryPrimitives.ReverseEndianness(BitConverter.ToInt64(b) & 0x0000ffffffffffff));

                Console.WriteLine(ret);

                return ret;

            });

        Console.WriteLine(foundIndex);

    }

}