Re: IOS floating point performance
Re: IOS floating point performance
- Subject: Re: IOS floating point performance
- From: Sandy McGuffog <email@hidden>
- Date: Thu, 08 Aug 2013 21:06:44 +0200
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@hidden> 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@hidden> 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
>
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