Thanks Mike. On Thu, Apr 9, 2009 at 11:55 AM, Michael McCandless < luc...@mikemccandless.com> wrote:
> On Wed, Apr 8, 2009 at 11:22 PM, Shai Erera <ser...@gmail.com> wrote: > > Hi > > > > I used ArrayUtils.getNextSize recently to expand an array to a new size. > > When I read the documentation (the inline in the method), I saw this: > > > > "The growth pattern is: 0, 4, 8, 16, 25, 35, 46, 58, 72, 88, ..." > > > > I'm not sure if I'm misunderstanding the comment, or if there is a bug in > > the implementation. The way I understand it, the method will always > return > > 0, 4, 8, 16 ... values, such that if I pass 9-15 I'll always get 16. But > > then I noticed that if I pass 15, I get back 22 (which is the result of > the > > computation). Is it a bug? > > Note: this was lifted from Python's sources, in how it grows a list as > you append elements to it (credit/license reference for this is at the > end of Lucene's LICENSE.txt). > > It's fine that you got 22 back. > > The comment really means "if you only use getNextSize to get the > series of sizes" that's the sequence that's followed. If you pass in > your own size (not previously returned by getNextSize), you'll get a > different sequence, which is fine. > > > Also, while on that subject - why don't we return the closest power of 2? > > I'm not familiar with that expansion policy, and I don't know how it will > > behave for large values. I guess a pure "closest power of 2" is not too > good > > since for very large values it will return twice the size which is not > too > > good, but we can have a smarter impl. which checks the value passed and > > returns a new number in chunks of let's say 1K, when the passed in number > is > > very large (let's say 1M). > > It's designed to grow exponentially, but at a more lenient rate than > 2X which indeed for large values is costly. > > For smallish values it grows aggressively, then for larger values it > converges to an oversize of 1/8th (12.5%). > > > If you think that's useful, I can open an issue and either change the > method > > impl, or add a new one getNextPower2Size. > > I don't think we need to change it. Python has converged on this > approach over the years ;) > > Mike > > --------------------------------------------------------------------- > To unsubscribe, e-mail: java-dev-unsubscr...@lucene.apache.org > For additional commands, e-mail: java-dev-h...@lucene.apache.org > >
