inaccurate probabilities in IteratorRandom::choose() #1058
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kazcw
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Oct 11, 2020
f64 reciprocal is inexact, with residuals on the order of 1 / 2^54. For example: the probability gen_bool(1.0 / 3) == true is: 6004799503160661/18014398509481984 Using gen_range is exact for all values of `consumed`. NOTE: this is a value stability-breaking change fixes rust-random#1058
kazcw
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Oct 13, 2020
f64 reciprocal is inexact, with residuals on the order of 1 / 2^54. For example: the probability gen_bool(1.0 / 3) == true is: 6004799503160661/18014398509481984 Using gen_range is exact for all values of `consumed`. NOTE: this is a value stability-breaking change fixes rust-random#1058
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IteratorRandom::choose()uses a floating-point reciprocal to calculate probabilities. f64 reciprocal is an inexact operation with residuals on the order of 1 / 2^54.For example: the probability of
gen_bool(1.0 / 3) == trueis: 6004799503160661/18014398509481984, which differs from 1/3 in the 17th digit.An exact implementation of
choosewould be possible withgen_range.The text was updated successfully, but these errors were encountered: