# What algorithm was used for function ippiDFTFwd_RToPack_32f_C1R and what is the algorithm complexity?

## What algorithm was used for function ippiDFTFwd_RToPack_32f_C1R and what is the algorithm complexity?

What algorithm was used for function ippiDFTFwd_RToPack_32f_C1R?

And what is the algorithm complexity? like the method in FFTW?

I tried to increase the image size for the ippiDFTFwd_RToPack_32f_C1R, the execution time is not monotone increasing (of couse, 2^n is of the minimum execution time). Is there any theory analysis of the algorithm complexity for ippiDFTFwd_RToPack_32f_C1R? Many thanks!

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>>...What algorithm was used for function ippiDFTFwd_RToPack_32f_C1R?

Intel never releases details on internals of some API / algorithms and a generic answer could be as follows: a DFT-like algorithm is used.

Please try to search for articles or application notes on Intel web-site related to DFT processing.

Note: I checked my collection of Intel articles and I have these two:

Split-Radix FFT.17649.pdf
SSE in a Fast DCT Algorithm.40981.pdf

Hi, Sergey, could you send me the articles? I tried to search but can not find the pdf files.

Split-Radix FFT.17649.pdf
SSE in a Fast DCT Algorithm.40981.pdf

Many thanks!

Hi,

IPP DFT is based on vector/image length/size decomposition on primes. Prime factors that have special code branches are 2,3,5,7,11,13. For powers of 2 (FFT) supported radixes are 2,4,8,16 (depends on architecture - radix-8 is supported on Intel64, radix-16 - on Xeon-Phi only). For lengths/sizes that can't be decomposed on these primes (or for reminder parts) - convolution based algorithm is used. In general case you may consider algorithm complexity as ~5*n*log2(n) arithmetic operations per 1 call (1D case, n==vector length).

Regards, Igor

>>...could you send me the articles? I tried to search but can not find the pdf files.
>>
>>Split-Radix FFT.17649.pdf
>>SSE in a Fast DCT Algorithm.40981.pdf

Yes and I'll do it later today.

>>>>...could you send me the articles? I tried to search but can not find the pdf files.
>>>>
>>>>Split-Radix FFT.17649.pdf
>>>>SSE in a Fast DCT Algorithm.40981.pdf
>>
>>Yes and I'll do it later today.

Here they are.

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>>>>Split-Radix FFT.17649.pdf

Here is a zip-file with sources.

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