Question

I am looking for performance efficient ways to compare two byte[] for equality. Sizes are above 1 MB, so the overhead for each array element should be minimized.

I aim to beat the speeds of SequenceEqual or a hand-coded for-loop over every item, by avoiding the repetitive bound checks for both arrays. In the same way that Array.Copy could lead to fast memcpy, what will lead to a memcmp?

Answer 1

If performance really matters then the fastest way to do it is by using the CRT library included with every version of Windows. This code takes ~51 msec on my poky laptop, works on 64-bit machines too:

using System;
using System.Runtime.InteropServices;
using System.Diagnostics;

class Program {
  static void Main(string[] args) {
    byte[] arr1 = new byte[50 * 1024 * 1024];
    byte[] arr2 = new byte[50 * 1024 * 1024];
    var sw = Stopwatch.StartNew();
    bool equal = memcmp(arr1, arr2, arr1.Length) == 0;
    sw.Stop();
    Console.WriteLine(sw.ElapsedMilliseconds);
    Console.ReadLine();
  }
  [DllImport("msvcrt.dll")]
  private static extern int memcmp(byte[] arr1, byte[] arr2, int cnt);
}