fix(tdigest): return max when the last centroid has weight 2 - #188
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jaideeppyne wants to merge 1 commit into
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jaideeppyne wants to merge 1 commit into
jaideeppyne wants to merge 1 commit into
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The right-tail division is 0/0 for that weight. Round the rank weight before subtracting it so arm64 does not fuse the multiply and skip the tail.
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Quantile's right tail divides bylastWeight/2 - 1. That denominator is zero when the last centroid weighs 2, and the only rank that reaches the branch (one unit of weight below the total) has a zero numerator as well, so the result is NaN.Java and Rust already return the stored maximum in this case. This does the same.
The rank weight is also rounded before it is subtracted from the total. On arm64 the compiler otherwise fuses that multiply and subtract, skips the right tail, and returns a value past the maximum (40 for a sketch whose maximum is 20).
Tests:
go test ./tdigest/. The new case builds centroids of weight 10 and 2 and checksQuantile(11/12)is the maximum.