Cleanup BitMapper sizeof type

[IDisposable]

In fix for #86740, the newly introduced internal BitMapper in DiagnosticsHelper.cs uses an internal Span<ulong> however a couple of sizeof() used long. While these types are the same size, this is a minor correctness/cleanliness change with no actual code delta. Also added a comment to document the right-shift by 6 bits.

[IDisposable]

Wondering if we care about TARGET_64BIT building (e.g. should we be using ulong for 64-bit builds and uint for 32-bit builds). This is something we do care about in BitOperations.PopCount for example.

[ghost]

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Issue Details

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In fix for #86740, the newly introduced internal BitMapper in DiagnosticsHelper.cs uses an internal Span<ulong> however a couple of sizeof() used long. While these types are the same size, this is a minor correctness/cleanliness change with no actual code delta. Also added a comment to document the right-shift by 6 bits.

Author:	IDisposable
Assignees:	-
Labels:	area-System.Diagnostics, community-contribution, needs-area-label
Milestone:	-

[IDisposable]

Additionally, wondering if there is value in making this a System.Collection publicly visible class (can a public "class" even be a struct?)

[IDisposable]

Comments @noahfalk or @tarekgh?

[noahfalk]

Wondering if we care about TARGET_64BIT building

Performance differences are possible, but functionally it shouldn't matter.

Additionally, wondering if there is value in making this a System.Collection publicly visible class

Given that we already have BitArray and BitVector32, I'm skeptical there are many .NET users who would benefit from another. I don't rule it out, but also no plan to proactively pursue it.

(can a public "class" even be a struct?)

Assuming that you used 'public class' to mean any public type in .NET then sure, BitVector32 is an example that is struct and there are many public structs in .NET. If you meant 'class' as in the C# keyword, then no, struct and class are mutually exclusive.

[noahfalk]

Seems fine to me, but @tarekgh owns the code so his call if he wants the change.