Enable reusing fft plans

[IanButterworth]

Requires

• v1.0.0: Add RCpair copy! for complex. Rename region->dims. Remove deprecation. HolyLab/RFFT.jl#17

TODO:

• Merge v1.0.0: Add RCpair copy! for complex. Rename region->dims. Remove deprecation. HolyLab/RFFT.jl#17
• Register RFFT.jl in General
• Tidy (remove manual RFFT add, remove demo)
• Settle on naming/API i.e. should this be setup via Algorithm.FFT(img, kernel, border)?
• Docstrings

---

Because they are not threadsafe FFTW FFT plans are behind a lock. They should be reusable for same-sized images and kernels, so this is WIP towards exposing a way to provide plans, so that imfilter! can be run concurrently on julia threads without lock conflict.

Note that this is using JuliaLang/julia#52883 to count conflicts.

There's a demo temporarily in this PR.

Before it hits 34255 lock conflicts

% FFTW_NUM_THREADS=1 BLAS_NUM_THREADS=3 ../julia/julia --project -t6,1 -q
julia> include("demo.jl")
warm run of benchmark(mats): 5.483911 seconds (2.14 M allocations: 10.671 GiB, 16.62% gc time, 34255 lock conflicts)

This PR removes all but the lock conflicts from the singlular plans, which could be moved out of the for loop

% FFTW_NUM_THREADS=1 BLAS_NUM_THREADS=3 ../julia/julia --project -t6,1 -q
julia> include("demo.jl")
warm run of benchmark(mats): 2.440659 seconds (478.12 k allocations: 7.888 GiB, 21.53% gc time, 8 lock conflicts)

[IanButterworth]

Ok, I think this seems reasonable now. @timholy would you mind reviewing for general design and I can add tests & docs if you agree

[timholy]

I confess I haven't thought about these plans in ages (the code I linked earlier was probably written in the Julia 0.1 days), but nothing bad jumps out about this. Thanks for doing it!!

[IanButterworth]

Comparing buffered vs standard I get different values here

ImageFiltering.jl/src/imfilter.jl

Lines 875 to 877 in 78044e7

	B = complex(planned_rfft1(A)) * FFTW.AbstractFFTs.to1(A)
	_B = rfft(A)
	@show B[1:4] _B[1:4]

B[1:4] =  ComplexF32[3065.7727f0 + 113.279686f0im, -254.48924f0 - 85.513504f0im, -369.77383f0 - 146.0826f0im, -267.98865f0 - 201.43063f0im]
_B[1:4] = ComplexF32[4595.6045f0 + 0.0f0im,         3.6047888f0 + 15.441383f0im,  14.378552f0 - 19.552792f0im, -18.684448f0 - 19.284311f0im]

My trial and error phase of debugging isn't being very fruitful, so I think I'll wait for review. @timholy if you happen to have time

[mkitti]

Commeting to remind myself to take a look

[timholy]

Nothing jumps out as a serious problem just from a read through the code, but it's probably been a decade since I put the serious work into writing RFFT.jl (it used to be part of a more monolithic repository so the git history may not reflect that). Do the disagreements only arise when you use multiple threads?

[codecov]

Codecov Report

Attention: Patch coverage is 96.11650% with 4 lines in your changes missing coverage. Please review.

Project coverage is 92.36%. Comparing base (01e99cd) to head (037ac37).

Files with missing lines	Patch %	Lines
src/ImageFiltering.jl	80.00%	2 Missing ⚠️
src/imfilter.jl	98.91%	1 Missing ⚠️
src/utils.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #271      +/-   ##
==========================================
+ Coverage   91.86%   92.36%   +0.50%     
==========================================
  Files          12       12              
  Lines        1672     1769      +97     
==========================================
+ Hits         1536     1634      +98     
+ Misses        136      135       -1     

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[IanButterworth]

Ok. Tests are passing here.

Note that planned_fft doesn't support non-float eltypes currently because RFFT.RCpair only supports floats (and other reasons, I guess).

However, demo.jl still fails

f1[1:4] = [0.11624783622854669, 0.15113825707056688, 0.16887924282352731, 0.20249257393260642]
f2[1:4] = [0.17744583830964283, -0.0655415564571991, -0.10802786527654895, 0.11185075216343188]
ERROR: LoadError: f1 !≈ f2

[timholy]

Thanks for this! Not only is the new functionality appreciated, but the various cleanups are too.

I haven't played with this myself, but does demo pass now? If so, it seems like you're almost over the hump. I don't see anything objectionable here (assuming you'll get to a point of full test coverage for the new functionality), so feel free to run with this.

[IanButterworth]

@timholy I got unstuck here with the help of AI.. (claude 4 agent mode in vscode copilot, see dev/debug_planned.jl for the debugging investigation I got it to put together along the way)

Tests pass and coverage looks good to me, but there might be more correct ways of doing the various transforms.