Fixed HashCode not being Case Insensitive, Improved HashCode Performance & Use SIMD/Intrinsics Code from External Library (Fixes #25)

[Sewer56]

Changelog

Replaced String Hash Function with Custom One tailored for Lowercase

• Optimised for ASCII inputs hashing as lower in-place. non-ASCII inputs fallback to first converting to lowercase before hashing.

• To give some context, for strings, .NET uses a cryptographically secure, DoS resistant hash function.

  • However it's piss slow...

• It slow enough that Dictionary and HashSet are hardcoded in the runtime to use a different, non-DoS resistant function if the key is typeof(string). (Hint: I checked that function out, it's DJB2 w/ 2 hashes, mixed at the end)

• Unfortunately you can't use that function 😊 at all, because it's internal, and because RelativePath / AbsolutePath aren't string, you're forced to use the slow one; which is a no-no for us.

• For a typical AbsolutePath to a file within game folder (~120 characters), the improvement in hashing speed is ~8-12x. (Depending on AVX2 availability)

• For a typical RelativePath for a file within game folder, or a file segment in a dictionary (~8-12 characters), the improvement is around ~2.3x.

• Hash quality is a bit lower/more collision prone, however the time save on hashing heavily outweighs the penalty spent on the occasional moment there's 1 more linear probe in .NET Dictionary (BCL dict uses linear probing). This applies even when used with short <8 character file paths.

• For the curious, you can find the relevant benchmarks here.

Moved fancy SIMD/Intrinsics Code

• Removed fancy SIMD and Intrinsics code from this library.

• Now using the originals from Reloaded.Memory, where I originally copied them from.

• For context: It's a lightweight, high performance library for low level memory manipulation & zero cost abstractions, created/maintained by me. Mostly used in game mods & tools [around 200 projects use it], and also has stable API.

• This should make maintenance easier, hopefully. (Removes ~1700 LoC from the repo)

• The only new code that was specifically written for this PR is the aforementioned lowercase variant of custom string hash.

• Note: This is a breaking change, because some of these were public APIs previously. However fixing any relevant code should be easy as the API names should not have changed, so it's just a matter of adding/replacing a namespace.

Improved AbsolutePath.Equals

• Changed order of Equals comparisons in AbsolutePath.Equals.
  • Now compares FileName first, instead of directory.
  • Statistically speaking, the file name is more likely to be different faster than directory is. So this is an improvement.

Other

• Added Sanity Tests to ensure GetHashCode and Equals are case-insensitive for RelativePath & AbsolutePath.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (29ddf3f) 85.64% compared to head (e5aaa7a) 86.71%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
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+ Coverage   85.64%   86.71%   +1.07%     
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  Files          44       42       -2     
  Lines        2939     2861      -78     
  Branches      507      494      -13     
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- Hits         2517     2481      -36     
+ Misses        357      324      -33     
+ Partials       65       56       -9     

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macOS	86.22% <100.00%> (+1.06%)	⬆️

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