IndexOfAnyInRange with invalid ranges behaves differently depending on hardware

[vcsjones]

Consider the following application:

using System;

class Program
{
    static void Main()
    {
        ReadOnlySpan<byte> data = [50];
        byte lowInclusive = 200;
        byte highInclusive = 100;

        int idx = data.IndexOfAnyInRange(lowInclusive, highInclusive);
        Console.WriteLine(idx);
    }
}

On an Apple M1 processor (and maybe other architectures), this will behave differently depending on if hardware intrinsics are available, or not.

Regularly:

❯ dotnet run                           
0

With intrinsics disabled:

❯ DOTNET_EnableHWIntrinsic=0 dotnet run
-1

Since this is not a "low level" SIMD API, I think it would be ideal if the invalid ranges produced consistent results (or threw an exception, but that is perhaps a breaking change).

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[EgorBo]

Reproduces on win-x64 as well, the vectorized path doesn't seem to check if highInclusive is less than lowInclusive (e.g. IndexOfAnyInRangeUnsignedNumber)

[vcsjones]

I should also clarify: Other range-based index methods like LastIndexOfAnyInRange exhibit the same behavior.

[EgorBo]

let's see what Copilot can do here without detailed guidance