On Mon, 4 Dec 2023 22:26:32 GMT, Brian Burkhalter <b...@openjdk.org> wrote:
>> fabioromano1 has updated the pull request incrementally with one additional >> commit since the last revision: >> >> Create RandomBigIntegers.java >> >> Create a benchmark to measure the performance of BigInteger(int, Random) >> constructor implementation. > > 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 About point 1. The behavior of `nextInt()` depends by the implementation of the Random object specified, which of course is not predictable. Furthermore, the claim that `nextInt()` invokes `nextLong()` by default and throws away the lower 32 bits is evidently denied by the facts: simply look at the last version of the method implementation in the class Random: https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/Random.java#L494 So, in the light of that, I think it's not worthwhile using `nextLong()` instead of `nextInt()`, it would only complicate the code. ------------- PR Comment: https://git.openjdk.org/jdk/pull/16817#issuecomment-1840727834
