StepTHn: do a pre lookup for the bin using a uniform grid

[ktf]

Rather than doing a O(log N) binary search for the correct bin, precompute a uniform index for a O(1) lookup and find the actual bin using a short linear search.

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• -> StepTHn: do a pre lookup for the bin using a uniform grid #15444
• StepTHn: speedup filling #15443

[ktf]

@jgrosseo with these two I gain 10% in performance for the Correlation business. On hyperloop the results seem to be compatible, for what I can tell. Can you validate and eventually merge?

[jgrosseo]

I can look into this next week...

[ktf]

@jgrosseo: I ran your script and did a comparison for both #15443 and this one.

The simple one (#15443) which simply gets rid of the repeated dynamic dispatch resulted in identical AnalysisRoot.root files (and by consequence, also dphi_corr.root files are identical).

This one was a bit more tricky, because a few bins were differing because of some rounding errors due slightly different bin finding logic. This was fixed and the logic is now exactly the same as TAxis::FindBin. The results are now identical, both for dphi_corr.root and for the actual AnalysisResults.root content.

I attach a PDF with the validation: dphi_comparison.pdf for this PR.

I think both PRs are ready to be merged.

[jgrosseo]

Thanks for the extensive validation. Fingers crossed :)

[ktf]

Yes, and it's monday, so we have a full week to fix it... :-D

[ktf]

discussed privately and merged.