.NET Fiddle

CSharp · Console

/Program.cs

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);
	}
}