Hello. Le mer. 13 févr. 2019 à 15:23, Alex Herbert <alex.d.herb...@gmail.com> a écrit : > > I am adding a new family of random generators in commons-rng. The > algorithms do not work when the seed state is all zeros [1]. What would > be best solution for an API. Here are some options: > > 1. Throw an exception.
-1 The core generators should (mis)behave like their reference implementation It is useful for experimenting and comparing. Also the doc mentions that the core generators should not be used directly. Non-"advanced" users should stick with the factory methods in "RandomSource" (where seed auto-generation will highly unlikely yield a zero state). > > 2. Fall-back to a known default seed that works. -1 Cf. above, this is done in "RandomSource". Caveat for those who choose their seed. > > 3. Allow it and users beware (this is the current behaviour for an > existing generator in the library with this defect). A generator may be > created that is broken (e.g. always returns zero). +1 > > 4. Allow exceptions from the constructor (to prevent misuse) -1 > but update > the recommended way of creating a generator to never fail. +1 [But it may not be possible to give this warranty.] > This is a > modification to the commons-rng-simple API method > RandomSource.create(RandomSource.XXX) to ensure that a seed created by > the library is never bad for the chosen algorithm. AFAIK it is not possible to ensure that a seed is "good". > > Option 1 is easy but may present a problem to the user of the library > who chooses a bad seed (or one is generated badly by chance). > > Option 2 ensures that illegal seeds can be used to create good generators. > > Option 3 allows creation of bad generators. This is a bug IMO. > > Option 4 should allow a user of the recommended API to never get a bad > generator or an exception. But direct use of the core API requires a > user beware approach as exceptions can happen is used incorrectly. The recommended API is "RandomSource" (or use at your own risk); hence the logic for ensuring, as much as possible, a good RNG must be done there (if not already implemented by the reference implementation, as is the case e.g. for "MersenneTwister"[1]). Best, Gilles [1] http://commons.apache.org/proper/commons-rng/commons-rng-core/apidocs/src-html/org/apache/commons/rng/core/source64/MersenneTwister64.html#line.156 > > > I am favouring option 4. > > > Feedback is welcome. > > Alex > > > [1] Many of the algorithms in the library can accept a zero seed for the > initial state. This is because they use additions in the algorithm to > propagate to the next state. The new family uses the Xor operator, bit > shifts and multiplications. If the initial state is all zero this just > remains at zero and the generator is broken. --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
