feat: add basic exponential histogram #1736
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Description
This PR introduces basic functionality for exponential histograms, similar to Python and JavaScript. Most of the code is adapted/copied from Python. The only missing feature compared to other languages is merging.
Exponential histogram merging aims to make bucket sizes consistent. With the current otel-ruby metrics collection mechanism, raw data is sent unmodified to the collector (e.g., from
@data_point).I think it's best to implement the merge feature on the collector side to reduce duplicate work and computation on the client side. Downscaling is implemented on the language side to adjust bucket sizes, avoiding out-of-range indices for very large or small numbers.
Test
Most test cases are copied from Python/JavaScript to ensure the correctness of mapping and downscaling.
I didn't add all test case from Python as I think some of the test cases are redundant (e.g. 0 increment, etc.) but please correct me if I am wrong.