From: Urabe Shyouhei <shyouhei@...>
Date: 2014-01-22T12:16:30+09:00
Subject: [ruby-core:59953] Re: [ruby-trunk - Feature #9425] [PATCH] st: use power-of-two sizes to avoid slow modulo ops

On 01/21/2014 11:38 AM, Eric Wong wrote:
>> https://github.com/shyouhei/ruby/commit/f7ca891
> 
> Thanks!  However, I wasn't able to show a difference with
> "make benchmark"[1].   Were you?
> 
> Perhaps rehash is not called often enough, and I think a branch
> inside the loop is difficult for the CPU to optimize.  I think
> the current dumb loop is very good for CPU pipelining and prefetch.

No, sorry I see no evident speedup.  When I wrote the patch I thought the
function was used for Hash#rehash, but it turned out Hash#rehash uses
something different (don't know why).  The optimization is valid I
believe but in fact used very rarely.