Why are the FFT outputs always zero for some specific point numbers when using FFTW with MKL

General Usage Performance
1

I’m using an Intel CPU with Julia 1.12. When my FFT size is 178848185, whether I do FFT or rFFT, the output is always all zeros. But if I use fftw provider, it works normally. This issue is very easy to reproduce. The code is:

using FFTW
using Random
FFTW.set_provider!(“mkl”)
println(fft(randn(178848185)))

Is this an MKL bug, or are there some usage limitations?

2

Can’t say I can reproduce it

julia> using FFTW

julia> FFTW.get_provider()
"mkl"

julia> any(iszero, fft(randn(178848185)))
false

(any looks a bit better than printing 100 million numbers to screen)

Writing a C program doing the same operation and linking to MKL would reveal that.