Adding Span IndexOf that takes an index and count

[ahsonkhan]

No description provided.

[ahsonkhan]

cc @KrzysztofCwalina, @davidfowl

[jkotas]

Where is the approved API proposal for this? What about the other overloads?

[jkotas]

If this is just a temporary hack until the Span codegen is fixed, you should keep it in corefxlab.

[KrzysztofCwalina]

Yeah, I agree corfxlab might be a better place for it. corfx APIs should represent what we are confident in shipping.

[davidfowl]

That's fine, will slicing + indexof ever be as fast as passing an index and count? I have some doubts about that.

while (span.Length > 0)
{
      int index = span.IndexOf((byte)'\n');
      if (index == -1) break;
      var line = span.Slice(0, index);
      span = span.Slice(index + 1);
}

VS

int index = 0;
while (index < span.Length)
{
      int lineIndex = span.IndexOf((byte)'\n', index, span.Length - index);
      if (lineIndex == -1) break;
      var line = span.Slice(index, lineIndex - index + 1);
      index += length.Length
}

Will that ever be within the ballpark?

[jkotas]

Yes, it should be pretty equivalent - once the JIT team implements the planned struct enregistration that handles Span well.

[davidfowl]

Wow, I look forward to seeing this. @ahsonkhan Can you make sure we have a benchmark for this scenario? It's pretty fundamental.

[ahsonkhan]

I have created it in the PR in corefxlab:

result = bytes.IndexOf(lookupVal, startIndex, count);

VS.

result = bytes.Slice(startIndex, count).IndexOf(lookupVal);

[jkotas]

I do not think it makes sense to replicate the worker method for this - you should use the existing public static int IndexOf(ref byte searchSpace, byte value, int length) method.

[ahsonkhan]

This PR can be closed. Opened one in corefxlab - dotnet/corefxlab#1278