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)) -Yonik
