On Fri, Dec 19, 2008 at 8:35 PM, Yonik Seeley <ysee...@gmail.com> wrote:
> On Fri, Dec 19, 2008 at 7:10 PM, Mike Klaas <mike.kl...@gmail.com> wrote: > > > > On 19-Dec-08, at 8:27 AM, Kay Kay (JIRA) wrote: > >> int newCapacity = (oldCapacity * 3)/2 + 1; > >> > >> +1 seems to be move away from 0, and keep incrementing the count. ( Hmm > .. > >> That piece of code - in Java 6 ArrayList can definitely make use of > bitwise > >> operators for the div-by-2 operation !!). > > > > Let's not go crazy here guys. This relatively trivial calculation is > only > > called log(n) times, and certainly uses bit ops after the jit gets its > hands > > on it. > > Log(n) point is well taken. > > The translation from "/2" to ">>1" can only really take place when the > compiler knows it's unsigned. This might be a simple enough case for > the compiler to figure it out, but who knows... it took forever (late > Java6) to generate native rotate instructions. > > Oh, and Kay, the simplest way to strength-reduce x*3/2 is (x+x/2) or > (x+(x>>1)) I agree. If we are doing any numeric calculations with the numbers predetermined - we might as well help the compiler generate the most efficient code, instead of human readable ease . (That can always go in the comments ). > > -Yonik >
