Comparing two byte arrays in .NET

How can I do this fast?

Sure I can do this:

static bool ByteArrayCompare(byte[] a1, byte[] a2)
{
    if (a1.Length != a2.Length)
        return false;

    for (int i=0; i<a1.Length; i++)
        if (a1[i]!=a2[i])
            return false;

    return true;
}

But I'm looking for either a BCL function or some highly optimized proven way to do this.

java.util.Arrays.equals((sbyte[])(Array)a1, (sbyte[])(Array)a2);

works nicely, but it doesn't look like that would work for x64.

Note my super-fast answer here.

Solution 1:

You can use Enumerable.SequenceEqual method.

using System;
using System.Linq;
...
var a1 = new int[] { 1, 2, 3};
var a2 = new int[] { 1, 2, 3};
var a3 = new int[] { 1, 2, 4};
var x = a1.SequenceEqual(a2); // true
var y = a1.SequenceEqual(a3); // false

If you can't use .NET 3.5 for some reason, your method is OK.
Compiler\run-time environment will optimize your loop so you don't need to worry about performance.

Solution 2:

P/Invoke powers activate!

[DllImport("msvcrt.dll", CallingConvention=CallingConvention.Cdecl)]
static extern int memcmp(byte[] b1, byte[] b2, long count);

static bool ByteArrayCompare(byte[] b1, byte[] b2)
{
    // Validate buffers are the same length.
    // This also ensures that the count does not exceed the length of either buffer.  
    return b1.Length == b2.Length && memcmp(b1, b2, b1.Length) == 0;
}