feat: add `fft/base/fftpack/ndarray/rffti` by gunjjoshi · Pull Request #13527 · stdlib-js/stdlib

gunjjoshi · 2026-07-18T01:50:32Z

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Resolves stdlib-js/metr-issue-tracker#1070.

Description

What is the purpose of this pull request?

This pull request:

adds fft/base/fftpack/ndarray/rffti, which will be the one-dimensional ndarry wrapper for fft/base/fftpack/rffti.

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This pull request has the following related issues:

[RFC]: add fft/base/fftpack/ndarray/rffti metr-issue-tracker#1070

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Read, understood, and followed the contributing guidelines.

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Used Gemini 3.5 Flash to search and understand working of ndarray wrappers.

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gunjjoshi · 2026-07-18T01:51:25Z

Opening a draft PR to discuss the implementation here, since this seems to be a bit different from existing ndarray wrappers.

gunjjoshi · 2026-07-18T01:59:44Z

+function rffti( arrays ) {
+	var workspace;
+	var N;
+
+	N = ndarraylike2scalar( arrays[ 0 ] );
+	workspace = arrays[ 1 ];
+	strided( N, getData( workspace ), getStride( workspace, 0 ), getOffset( workspace ) ); // eslint-disable-line max-len
+	return workspace;
+}


We can't directly send numelDimension( workspace, 0 ) here, as the length of the sequence to transform (N) is different from the size of the workspace array (2*N + 34).

gunjjoshi · 2026-07-18T02:04:28Z

@kgryte Let me know if the above looks good, or if I should make any changes here. I'll work on adding other files meanwhile.

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stdlib-bot · 2026-07-20T20:58:29Z

Coverage Report

Package	Statements	Branches	Functions	Lines
fft/base/fftpack/ndarray/rffti	$\\color{green}143/143$ $\\color{green}+0.00\\%$	$\\color{green}3/3$ $\\color{green}+0.00\\%$	$\\color{green}1/1$ $\\color{green}+0.00\\%$	$\\color{green}143/143$ $\\color{green}+0.00\\%$

The above coverage report was generated for the changes in this PR.

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gunjjoshi · 2026-07-20T21:12:33Z

+* var factors = slice( workspace, new Slice( 2*N, ( 2*N ) + 4 ) );
+* // returns <ndarray>[ 8, 2, 2, 4 ]
+*/
+declare function rffti( arrays: [ ndarray, float64ndarray ] ): float64ndarray;


I have used ndarray here (for N) instead of something like int32ndarray, since I didn't saw a similar use anywhere.

gunjjoshi · 2026-07-20T21:15:16Z

+	expectedTwiddles = new Float64Array( [ 0.7071067811865476, 0.7071067811865475, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+	expectedFactors = new Float64Array( [ 8, 2, 2, 4 ] );


Instead of using the full expected workspace array (which would be of length 2N+34), I have just initialized the twiddle and integer factors.

Sounds good.

gunjjoshi · 2026-07-20T21:18:00Z

+	expectedTwiddles = new Float64Array( [ 0.7071067811865476, 0.7071067811865475, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+	expectedFactors = new Float64Array( [ 8, 2, 2, 4 ] );


Since I am using these same 2 arrays in most of the tests, would it be better to move these to a separate // VARIABLES // section at the top? Or do we prefer this current way?

This way is fine.

kgryte · 2026-07-22T18:32:35Z

+*
+* var workspace = new Float64Vector( ( 2*N ) + 34 );
+*
+* var out = rffti( [ len, workspace ] );


Suggested change

* var out = rffti( [ len, workspace ] );

* var out = rffti( [ workspace, len ] );

kgryte · 2026-07-22T18:39:27Z

+*
+* -   The function expects the following ndarrays:
+*
+*     -   a zero-dimensional ndarray containing the length of the sequence to transform.


You'll want to update this order here and elsewhere.

kgryte · 2026-07-22T18:49:22Z

+		e = expectedFactors[ i ];
+		t.strictEqual( isAlmostSameValue( y, e, ulps ), true, 'within ' + ulps + ' ULPs. N: ' + N + '. y: ' + y + '. E: ' + e );
+	}
+


Add loop where you test that the non-indexed values are all zero.

Both the scratch space and all the elements which are in-between the indexed strided elements.

kgryte · 2026-07-22T18:50:47Z

+    > var twiddleFactors = {{alias:@stdlib/ndarray/slice}}( workspace, new {{alias:@stdlib/slice/ctor}}( N, 2*N ) )
+    <ndarray>[ ~0.707, ~0.707, 0, 0, 0, 0, 0, 0 ]
+    > var factors = {{alias:@stdlib/ndarray/slice}}( workspace, new {{alias:@stdlib/slice/ctor}}( 2*N, ( 2*N ) + 4 ) )


Suggested change

> var twiddleFactors = {{alias:@stdlib/ndarray/slice}}( workspace, new {{alias:@stdlib/slice/ctor}}( N, 2*N ) )

<ndarray>[ ~0.707, ~0.707, 0, 0, 0, 0, 0, 0 ]

> var factors = {{alias:@stdlib/ndarray/slice}}( workspace, new {{alias:@stdlib/slice/ctor}}( 2*N, ( 2*N ) + 4 ) )

> var s = new {{alias:@stdlib/slice/ctor}}( N, 2*N );

> var twiddleFactors = {{alias:@stdlib/ndarray/slice}}( workspace, s )

<ndarray>[ ~0.707, ~0.707, 0, 0, 0, 0, 0, 0 ]

> s = new {{alias:@stdlib/slice/ctor}}( 2*N, ( 2*N ) + 4 );

> var factors = {{alias:@stdlib/ndarray/slice}}( workspace, s )

kgryte · 2026-07-22T18:51:56Z

+* var factors = slice( workspace, new Slice( 2*N, ( 2*N ) + 4 ) );
+* // returns <ndarray>[ 8, 2, 2, 4 ]
+*/
+declare function rffti( arrays: [ ndarray, float64ndarray ] ): float64ndarray;


Suggested change

declare function rffti( arrays: [ ndarray, float64ndarray ] ): float64ndarray;

declare function rffti<T extends InputArray = InputArray>( arrays: [ T, typedndarray<number> ] ): T;

kgryte · 2026-07-22T18:53:16Z

+
+/// <reference types="@stdlib/types"/>
+
+import { ndarray, float64ndarray } from '@stdlib/types/ndarray';


Suggested change

import { ndarray, float64ndarray } from '@stdlib/types/ndarray';

import { typedndarray, floatndarray, genericndarray } from '@stdlib/types/ndarray';

kgryte · 2026-07-22T18:55:08Z

+
+import { ndarray, float64ndarray } from '@stdlib/types/ndarray';
+
+/**


Suggested change

/**

/**

* Input array.

*/

type InputArray = floatndarray | genericndarray<number>;

/**

kgryte · 2026-07-22T18:56:54Z

+// VARIABLES //
+
+var options = {
+	'dtype': 'int32'
+};
+
+


Suggested change

// VARIABLES //

var options = {

'dtype': 'int32'

};

kgryte · 2026-07-22T18:57:17Z

+	var len = scalar2ndarray( N, options );
+


Suggested change

var len = scalar2ndarray( N, options );

var len = scalar2ndarray( N, {

'dtype': 'int32'

});

kgryte · 2026-07-22T18:57:52Z

+var workspace = new Float64Vector( ( 2*N ) + 34 );
+console.log( ndarray2array( workspace ) );
+
+var len = scalar2ndarray( N, opts );


Suggested change

var len = scalar2ndarray( N, opts );

var len = scalar2ndarray( N, {

'dtype': 'int32'

});

kgryte · 2026-07-22T18:58:07Z

+var opts = {
+	'dtype': 'int32'
+};
+


Suggested change

var opts = {

'dtype': 'int32'

};

Applies to README, as well.

gunjjoshi added the METR Pull request associated with the METR project. label Jul 18, 2026

gunjjoshi commented Jul 18, 2026

View reviewed changes

Comment thread lib/node_modules/@stdlib/fft/base/fftpack/ndarray/rffti/lib/main.js Outdated

gunjjoshi commented Jul 18, 2026

View reviewed changes

gunjjoshi added 3 commits July 18, 2026 07:55

Merge branch 'develop' into ndarray/rffti

bfb49ed

gunjjoshi marked this pull request as ready for review July 20, 2026 20:46

gunjjoshi requested a review from a team July 20, 2026 20:46

stdlib-bot added the Needs Review A pull request which needs code review. label Jul 20, 2026

gunjjoshi commented Jul 20, 2026

View reviewed changes

kgryte reviewed Jul 22, 2026

View reviewed changes

		expectedTwiddles = new Float64Array( [ 0.7071067811865476, 0.7071067811865475, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
		expectedFactors = new Float64Array( [ 8, 2, 2, 4 ] );

	* var out = rffti( [ len, workspace ] );
	* var out = rffti( [ workspace, len ] );

	declare function rffti( arrays: [ ndarray, float64ndarray ] ): float64ndarray;
	declare function rffti<T extends InputArray = InputArray>( arrays: [ T, typedndarray<number> ] ): T;


		/// <reference types="@stdlib/types"/>

		import { ndarray, float64ndarray } from '@stdlib/types/ndarray';

	import { ndarray, float64ndarray } from '@stdlib/types/ndarray';
	import { typedndarray, floatndarray, genericndarray } from '@stdlib/types/ndarray';

-/**
+/**
+* Input array.
+*/
+type InputArray = floatndarray | genericndarray<number>;
+/**

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gunjjoshi commented Jul 18, 2026

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