On Tue, 5 Dec 2023 10:46:41 GMT, fabioromano1 <d...@openjdk.org> wrote:
>> Relaying comments from a colleague: >> >> 1. Half of the random bits are wasted by the use of `nextInt()`, which by >> default invokes `nextLong()` and throws away the lower 32 bits. Not sure if >> complicating the code to use all the 64 bits of `nextLong()` is worthwhile, >> though. >> >> 2. The way the random bits fill the magnitude array is different. This might >> break existing reproducible tests with seeded random number generators and >> fixed seed. Not sure if this is a real problem in practice, though. >> >> 3. There seems to be no test coverage that ensures the `BigInteger` >> invariant has either `mag.length == 0` or `mag[0] != 0`. While the code >> obviously ensures it, future changes might not, so it might make sense to >> have this aspect covered by a test. > > @bplb > 1. It would complicate the code, but even use the Random generator less > times, so the choice is between code more complicated or more calls to Random > generator. > > 2. This would be a problem only when, to make some comparisons, a test uses > the order of filling the magnitude used by the algorithm, I think. > > 3. If it has to be done, I think it should be by an assertion at the end of > `ranfomBits(int, Random)` method, since there is no way to access the class > fields for a method outside the package. @fabioromano1 About item 2. If a test external to OpenJDK uses a seedable random generator and initializes it with a fixed seed, and if it then compares the result with an expected value, after the change the test breaks. As mentioned, this might not be a problem in practice. About item 3. You can take a look at [this test](https://github.com/openjdk/jdk/blob/master/test/jdk/java/math/BigInteger/ByteArrayConstructorTest.java) to see how to access the fields using [this class](https://github.com/openjdk/jdk/blob/master/test/jdk/java/math/BigInteger/java.base/java/math/Accessor.java). ------------- PR Comment: https://git.openjdk.org/jdk/pull/16817#issuecomment-1840635876
