sorry for being vague. treating pixels as 64bit on amd64 as that is the natural size for the machine, vs using 32bits per pixel - 10 bits of r, g, and b or y, u, and v plus 2 spare leads to a significant speedup; where significant is a number lost in the mists of time.
i believe this speedup is due to the reduction in the rate of cache line refills, as forsyth described. -Steve On 6 May 2012, at 12:43 PM, Comeau At9Fans <[email protected]> wrote: > I've heard that 64-bit is not an immediate win over 32 for graphics and such, > but then again also heard that 32 bit is not the pits, and that it more or > less becomes a wash. So, in your case, what is is about 32 that makes it a > *significant* win, given that the space would have been used in either case > (I don't know if that's true, but assuming it is)? (And sorry if I've > connected "graphics and such" with image processing since it may be you're > doing something I'm not realizing and so we might be talking about different > things.) > > On Sun, May 6, 2012 at 5:20 AM, steve <[email protected]> wrote: > i think this is an often misunderstood fact, 32bit ints are, in my experience, > a significant win compared with 64bit when doing memory intensive work > - image processing in my case. > > -Steve > > > On 5 May 2012, at 06:48 PM, Charles Forsyth <[email protected]> > . > > if it's performance you're worried about, for programs that don't care > > about width, i'd expect 32 bits at least > > to match performance with 64 bits (if there's a measurable difference). for > > one thing, cache lines will contain > > more values, and several will be fetched at once when cache lines are > > filled. > > > > > > > -- > Greg Comeau / 4.3.10.1 with C++0xisms now in beta! > Comeau C/C++ ONLINE ==> http://www.comeaucomputing.com/tryitout > World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90. > Comeau C/C++ with Dinkumware's Libraries... Have you tried it? >
