[BUG] ContainsS returns different result to Contains

[Lukazoid]

void Main()
{
    var max = 999999;

    var nums = Enumerable.Range(0, max + 1).ToArray();

    Console.WriteLine(nums.ContainsS(max));
    Console.WriteLine(nums.Contains(max));
}

Outputs

False
True

Or another more simple example:

Console.WriteLine(new[]{1,2,3,4,5,6,7,8}.ContainsS(5));

It appears that .ContainsS fails for any of the last Vector<T>.Count elements when (haystack.Length % Vector<T>.Count) == 0

[yenmoc]

I tried your example on Unity but the same result is true

[Lukazoid]

@yenmoc Do the .NET SIMD types work under Unity? Are you sure it isn't just running without hardware acceleration (what's the result of Vector.IsHardwareAccelerated?)

Interesting if that is so as this definitely fails under .NET 6

[Lukazoid]

And this fails in particular when (nums.Length % Vector<T>.Count) == 0 so with Vector<int>.Count == 8 the following values of max all fail: 7, 15, 23 etc

And the needle to .ContainsS can be any of the last 8 values, e.g. Console.WriteLine(new[]{1,2,3,4,5,6,7,8}.ContainsS(5)); also outputs False.

[yenmoc]

Sorry my previous answer was because i didn't read your question carefully

In ContainsSIMD.cs

for (int i = 0; i < source.Length - count; i += count)
 {
                var v = new Vector<T>(source, i);
                if (Vector.EqualsAny(v, vectorValue))
                {
                    return true;
                }
  }

Change to

for (int i = 0; i <= source.Length - count; i += count)
 {
                var v = new Vector<T>(source, i);
                if (Vector.EqualsAny(v, vectorValue))
                {
                    return true;
                }
  }