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Non-determinism #3

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MariusVanDerWijden opened this issue Mar 10, 2019 · 0 comments
Open

Non-determinism #3

MariusVanDerWijden opened this issue Mar 10, 2019 · 0 comments

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@MariusVanDerWijden
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MariusVanDerWijden commented Mar 10, 2019

I've found out that the current libfqfft calculates different fft's depending on the amount of threads it is run in. E.g. the following produces two different outputs.

omp_set_num_threads( 4 );
_basic_parallel_radix2_FFT_inner<int> (v1, 5678, 2, 1);
omp_set_num_threads( 8 );
_basic_parallel_radix2_FFT_inner<int> (v2, 5678, 3, 1);
assert(v1 == v2);

The GPU implementation suffers from the same problem.
I think it has something to do with the padding that is applied here https://github.com/MariusVanDerWijden/gpusnark/blob/4bf8292ea79e05b9404f2742e83a587a32a0982e/fft_host.h#L71

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