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feat: add fft/base/fftpack/costi#13200

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feat: add fft/base/fftpack/costi#13200
gunjjoshi wants to merge 6 commits into
stdlib-js:developfrom
gunjjoshi:costi

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@gunjjoshi gunjjoshi commented Jun 29, 2026 •
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Resolves stdlib-js/metr-issue-tracker#831.

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Used gpt-5.1-codex-mini to review the package which was initially implemented manually, by copying over a similar package (fft/base/fftpack/cosqi) and modifying it.

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Gunj Joshi added 2 commits June 30, 2026 00:22
feat: add fft/base/fftpack/costi
35521d1 
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docs: use correct range in example
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@gunjjoshi gunjjoshi requested a review from a team June 29, 2026 18:58
@gunjjoshi gunjjoshi added Feature Issue or pull request for adding a new feature. METR Pull request associated with the METR project. labels Jun 29, 2026
@stdlib-bot stdlib-bot added the Needs Review A pull request which needs code review. label Jun 29, 2026
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gunjjoshi commented Jun 29, 2026

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The CI tests should pass once #13170 is merged. Marking this PR as a draft PR until then.

@gunjjoshi gunjjoshi marked this pull request as draft June 29, 2026 19:05
@stdlib-bot stdlib-bot removed the Needs Review A pull request which needs code review. label Jun 29, 2026
gunjjoshi and others added 3 commits July 6, 2026 18:39
@gunjjoshi
Merge branch 'develop' into costi
619d94f
@gunjjoshi
docs: update docs
5c6523f 
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@kgryte
Merge branch 'develop' into costi
adbc56c
@kgryte kgryte marked this pull request as ready for review July 7, 2026 01:06
@stdlib-bot stdlib-bot added the Needs Review A pull request which needs code review. label Jul 7, 2026
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stdlib-bot commented Jul 7, 2026

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@kgryte kgryte removed the Needs Review A pull request which needs code review. label Jul 7, 2026
kgryte
kgryte reviewed Jul 7, 2026
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Comment thread lib/node_modules/@stdlib/fft/base/fftpack/costi/lib/main.js
iw = offsetW;
for ( i = 1; i < ns2; i++ ) {
fk += 1.0;
sc = sincos( fk * dt );

@kgryte kgryte Jul 7, 2026

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You need to be using sincos.assign here with a WORKSPACE buffer. Otherwise, you are allocating a new 2-element array for each invocation. It is okay to write to this temporary workspace given that you need to multiply the factors by two. Otherwise, write directly to workspace and then do workspace[ j ] *= 2.0.

If you do the latter, cache the index computations. But also, why are you doing both addition and multiplication for indices? You should be doing iw += strideW. For the other index, define a separate iw variable and do iwc -= strideW, since it seems like you are decrementing the pointer.

In short, I suggest making your pointer arithmetic logic cleaner.

kgryte
kgryte reviewed Jul 7, 2026
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Comment thread lib/node_modules/@stdlib/fft/base/fftpack/costi/lib/main.js
* ↓ ↓ ↓ ↓
* | sine/cosine table | scratch/workspace | twiddle factors | radix factor table |
* ↑ ↑ ↑ ↑
* i = 0 ... N ... 2N-1 ... 3N-2 ...

@kgryte kgryte Jul 7, 2026

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Is it me, or does this table layout feel off? I feel like the scratch/workspace should start at 2N not 2N-1 and the radix factor table at 3N, not 3N-2. Otherwise, you don't need 3N+34 elements; you only need 3N+32 elements. I get that we are passing N-1 to rffti, so that is where the alignment issues come from, but it is still a bit odd to my eye.

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kgryte requested changes Jul 7, 2026
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Left initial comments.

@kgryte kgryte added the Needs Changes Pull request which needs changes before being merged. label Jul 7, 2026
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[RFC]: add fft/base/fftpack/costi

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