Avoid panics in Binomial BTPE sampler by using u64 values #43
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benjamin-lieser
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Dec 14, 2025
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Thank you a lot, this looks good.
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You say that even the low significant bits are now correctly distributed. Should we remove the disclaimer from the documentation? |
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No, #47 only checks that the least significant bit is correctly distributed for |
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CHANGELOG.mdentrySummary
This fixes a panic that can occur when the parameter
nfor theBinomialsampler is larger thani64::MAX.Motivation
This should resolve #21 .
Details
The key variable which previously used
i64inbinomial::btpewasy, the random coordinate in 0..=n on which the BTPE algorithm performed rejection sampling. Sincenis in0..u64::MAX,yshould also be inu64::MAX.This is a value-breaking change, because e.g. the code now does the float->int cast on the value
x_l + v.ln() / lambda_lafter checking whether the value is <= 0, instead of before. I don't think this sort of change in boundary rounding should cause any issues (and it may make the sampled distribution closer to the actual target.)I am looking into writing a test to confirm this is OK, but it may be a few weeks before it is ready.(Tested, the new version actually fixes a boundary issue, see test for it in #47.)