2016-05-24 11:03 GMT+02:00 Sven Van Caekenberghe <s...@stfx.eu>: > > > On 24 May 2016, at 10:55, Thierry Goubier <thierry.goub...@gmail.com> > wrote: > > > > Hi Sven. > > > > Using '((self + upper) / 2 ) truncated' seems to be a little bit faster > than 'self + upper bitshift: -1'. > > Is it ? >
Yes, just not by much and it avoids explaining that we use bitshift: there because n << 1 is usually much faster in C with a lousy compiler on a micro-controller. > > Even so, you probably agree that that calculation involving the bounds > that are not large integers is totally irrelevant in the light of the heavy > multiplications of large integers with thousands of digits, no ? > Then there is no reason to use a cryptic optimisation that doesn't optimise anything, no? > > That is why I also said that the recursion cost is (probably) acceptable. > > Anyway, if you want to freak out, go read the Fast Factorial Functions > website mentioned at the end > > http://www.luschny.de/math/factorial/FastFactorialFunctions.htm > > It is totally humbling (for me anyway) > No. High performance versions of numerical/signal/image/video processing codes are so complex usually for performance reasons that such a list is not surprising. The cleverness of some of the solutions are humbling, yes. To be able to make such a difference as you did with a few lines, however, is significant. Because it makes it easily integrated. Thierry > > > Thierry > > > > > > > > 2016-05-24 9:57 GMT+02:00 Sven Van Caekenberghe <s...@stfx.eu>: > > I just published a short, introduction level article, > > > > Speeding up factorial computation by changing the order of > multiplications. > > > > This is a story about a small, seemingly innocent code change that > speeds up a very simple computation. It is pretty magical and serves as an > example of how things are not always what they seem. > > > > > https://medium.com/concerning-pharo/speeding-up-factorial-computation-by-changing-the-order-of-multiplications-f4da3a5576da#.l3nrk9oax > > > > Enjoy, > > > > Sven > > > > -- > > Sven Van Caekenberghe > > Proudly supporting Pharo > > http://pharo.org > > http://association.pharo.org > > http://consortium.pharo.org > > > > > > > > > > > > > > >
