On 8 Aug, 2013, at 3:28 PM, Kevin Meaney <[email protected]> wrote: > I could well be wrong as I'm working from ancient memory but I believe c > upgrades floats to doubles to perform calculations and then if result is > stored in a float it will chuck away precision at time of assignment to the > float. > > I would repeat the recommendations of other to try using vlib. > > I gather from original question when OP referred to narrowing down to a few > functions that this was achieved by profiling. > > Kevin >
shouldn't do that as long as one uses the correct functions, ie sinf() and cosf(). Indeed if you just use sin() and cos() it will upgrade them to doubles and then cast them back down again, getting yet slower in the process than it was before. Without seeing the algorithm it's hard to say for sure but the OPs comment that float gave 'completely wrong answers' feels a bit odd. You'd have to have a very long string of calculations for the error between floats and doubles to add up to something which is 'completely wrong'. Could happen, but I'd look for bugs before discarding floats totally. I'd also probably look see if there's another algorithm, or if you can seed one day with the data from the previous/next one and start close to the right answer. Regrettably OpenCL hasn't made it to iOS yet, dumping massively parallel calculations like this onto the GPU can work wonders although I'm not well-enough versed with it to say whether the trig performance on a GPU sucks enough to make it not worthwhile. One last option is not to require a month at a time to be calculated. Much like populating UITableViews, if you can focus on the day someone's looking at right now and get that one done first, you can always calculate a few likely next ones in the background. App looks super responsive, under the water it's paddling like a crazed duck but always prioritizing the thing you need on screen right now. That is sometimes just a matter of changing the UI a bit. Another last option is to pre-calculate a load of this data, see if there is a bulk of the calculation which is say independent of the user's location, work that out and cache it, then finish the calculation off for the user's actual position. Again this all depends on exactly what you're trying to do. _______________________________________________ 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]
