David, Why don't you increment T by a little bit in each iteration, say by jj/1000., to prove that no optimization is occurring? I would do it but I develop for Mac OSX only.
Tom Wetmore On Aug 8, 2013, at 3:59 PM, David Rowland <[email protected]> wrote: > I ran it in Debug mode which should turn off most optimizations. I ran the > loop 100 times and then 200 times. The latter took almost exactly twice the > time as the former. The results are saved in instance variables of the C++ > class this belongs to. > > > On Aug 8, 2013, at 12:06 PM, Sandy McGuffog <[email protected]> wrote: > >> Be careful using that code as a test; a good optimizing compiler could pick >> up that sin is a library function without side effects, and no result is >> saved, and optimize that loop to two calls to adjustValueRadians. >> >> Sandy >> >> On Aug 8, 2013, at 8:17 PM, Thomas Wetmore <[email protected]> wrote: >> >>> David, >>> >>> Those are lightening speeds. So I agree with you wholeheartedly -- there is >>> no sense in working on a custom table-driven approach. The current approach >>> must already be table-based with speeds like that. >>> >>> Tom Wetmore >>> >>> >>> On Aug 8, 2013, at 1:26 PM, David Rowland <[email protected]> wrote: >>> >>>> I wrote an app that calculates the positions of Sun and Moon and other >>>> information as well. The heart of the Moon calculation is this. I added a >>>> loop around it and called a stopwatch at the beginning and end. >>>> >>>> startTime(); >>>> for (int jj = 0; jj<100;++jj) >>>> { >>>> //in radians >>>> double lambda = 3.81040282295402 + 8399.70910754626 * T >>>> + 0.109781209950443 * sin(adjustValueRadians(2.35619449019234 + >>>> 8328.69146829639 * T)) >>>> - 0.022165681500328 * sin(adjustValueRadians(4.5256387504213 - >>>> 7214.06294691607 * T)) >>>> >>>> One hundred times through this loop, on my iPhone 5, took about 0.0028 >>>> seconds. Two hundred times took about 0.0056 sec. >>>> >>>> I infer that one pass takes about 0.000028 seconds, or 28.0 microseconds. >>>> >>>> The functions are probably very carefully written and could not be >>>> improved by table lookups, vector libraries, etc. That is barking up the >>>> wrong tree. >>>> >>>> David _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
