Re: sin() optimization on PowerPC and Intel
Re: sin() optimization on PowerPC and Intel
- Subject: Re: sin() optimization on PowerPC and Intel
- From: "Andy O'Meara" <email@hidden>
- Date: Tue, 27 Jun 2006 13:16:27 -0400
- Thread-topic: sin() optimization on PowerPC and Intel
Some comments on the table method...
You can make your table much smaller if you do a linear interp method,
because it buys you a good chunk of precision. The resulting smaller size of
the table means memory bandwidth, at the cost of doing another load, two
mults, and an add. Clearly the performance gain (or loss) depends on the
hardware and compiler.
In any case, be sure yo use lrint() to convert your floats to indexes
(instead of a cast)--that's a biggie.
On 6/27/06 10:38 AM, "Bob Lang" <email@hidden> wrote:
> Hi
>
> If you're looking for fast execution speed then I'd be tempted to set
> up a large array and use it to store pre-computed sine values. This
> converts each calculation into a simple and fast look up operation.
> Of course, you only need to store one quarter of the cycle as the
> remaining three quarters can be easily obtained from the stored first
> quarter.
>
> If you hold (say) 900 separate points, then you can store each sample
> to a precision of 0.1 degree, which may already be sufficiently
> accurate for your application. Obviously, you can get better
> accuracy by using a bigger array and/or using a simple linear
> interpolation technique on two adjacent samples.
>
> Bob
> --
> On 26 Jun 2006, at 16:37, Artemiy Pavlov wrote:
>
>> Hello all!
>>
>> I have the following problem. XCode 2.2, Mac OS 10.4.6 on Intel.
>>
>> I created a sin() function replacement using four first members of
>> the Taylor series - works perfectly like the standard sin() (the
>> thing is that I need a very pure sine for FM purposes, so other
>> models do not work ear-wise).
>>
>> But the thing is that it doesn't work any faster than the standard
>> sin() function... It's not optimized with assembly language, but
>> anyway has no division operations and all coefficients are pre-
>> computed. I heard that on Intels the sin() function is actually
>> implemented in CPU instructions, and that is why it works so fast.
>> Is this true?
>>
>> So the question is - should I determine the CPU type for my
>> universal app and use sin() on Intel and custom sin() on PPC? If
>> so, are there any #define's available to be able to branch the code?
>>
>> Thanks!
>>
>>
>> All the best,
>>
>> Artemiy Pavlov
>> Sineshine http://sineshine.com
>>
>>
>>
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>
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