uniform_real_distribution: fix boundary so values are really [a,b) instead of [a,b] #596
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Copied this assertion from boost::random::uniform_real_distribution.
Currently b::c::r::uniform_real_distribution can produce a variate equal to the upper bound, which is wrong: it is supposed to (and claims to) produce values in [LO,HI), not [LO,HI], but when the random unsigned int draw equals UINT_MAX (or values close to it, with the rounding introduced by RealType = float), we get the upper limit, HI. This commit applies nextafter to the result to shift the result towards LO by the smallest amount possible, which therefore ensures that our maximum is now the largest representable value that is strictly less than HI. If we generate a value of LO (from a random uint of 0), we end up calling nextafter(LO, LO), which equals LO, so this will indeed conform to the [LO,HI) interval.
jagerman
changed the title
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Just 15 minutes ago I pushed the same PR. Well without the assertion |
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Yeah, I just noticed that. Closing this one. |
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I'll add the assert. It's a good idea. |
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Use the same nextafter approach from boost::compute::random::normal_distribution to eliminate the possibility of getting a draw equal to b, so that we really do produce [a,b) values, as currently documented (and desired).