Faster StartsWithSegments Ordinal check

[benaadams]

Framework's call to native comes with a cost

Before

After

[benaadams]

As an aside; the sets and whatnot have high costs as they are also doing dictionary lookups; typecasts and initalizing the feature cache

[halter73]

Do you have any thoughts @Tratcher?

[davidfowl]

Not a fan of this. Looks pretty unmaintainable. Is it really worth it? Can we make a change like this in corefx instead?

[benaadams]

Would be change to coreclr https://github.com/dotnet/coreclr/blob/master/src/mscorlib/src/System/String.cs#L2562

Will propose.

[halter73]

@davidfowl No less maintainable than GetAsciiString 😛

I see your point though. This is something probably done once per request at most, and I doubt most apps are even going to specify StringComparison.Ordinal.

[benaadams]

@halter73 The crazy is currently localized to one project :)

[benaadams]

Raised PR in coreclr dotnet/coreclr#2667