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Re: IOS floating point performance
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Re: IOS floating point performance


  • Subject: Re: IOS floating point performance
  • From: Rick Mann <email@hidden>
  • Date: Wed, 07 Aug 2013 14:17:48 -0700

A few things:

- The little ARM in the iPad 3 is nothing compared to your desktop. Not only is it not as fast, it doesn't have the memory bandwidth. Also, an iPad 4 will be twice as fast.
- make sure you're running optimized code. You can set optimization flags on individual files (that's what I do in our compute-heavy code, so I can run debug releases for the UI but leave the computation optimized).
- Find a way to compute less. Algorithmic optimizations are key here. Maybe a larger step size?
- Can you break up the work into multiple tasks? That will allow you to parallelize the work. At the very least, make sure you're doing it on a separate dispatch queue/NSOperationQueue so it doesn't block your main UI.

On Aug 7, 2013, at 13:50 , Trygve Inda <email@hidden> wrote:

> I have an app that is running slow. I have narrowed it down to several
> functions which are trig-intensive (used to calculate the position of the
> moon at a given moment and more specifically to calculate rise/set times).
>
> To calculate the position and rise/set times for a month on average,
> requires:
>
> 300 trig functions for position
> 24 points in time to find the correct set of three points
> 30 days
>  2 events
>
> Total of 432,000 trig functions (mostly sin and cos)
>
> On my iPad 3, this takes about 3 seconds, and on my desktop (2.3GHz
> Quad-core i7) it is nearly instantaneous.
>
> I am using doubles (not floats).
>
> What can I do to speed this up?
>
>
>
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--
Rick




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