DDSketch: A fast, fully-mergeable quantile sketch with relative-error guarantees 7 years ago
I did see that thread and that's what inspired the mapping with the quadratic interpolation.
To clarify though, DDSketch as defined in the paper uses the logarithmic mapping, as our main goal was to make the memory footprint as small as possible. See: https://github.com/DataDog/sketches-java/blob/1650d939f1485f...
The Java implementation abstracts out the index mapping. This let us add alternative ways to map values to indices and we added the method with the quadratic interpolation as it seems to be a good tradeoff between index computation speed and memory footprint.