feat: radf3, minor clean-up

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---

Author: gunjjoshi

lib/node_modules/@stdlib/fft/base/fftpack/lib/radb4.js

@@ -126,7 +126,7 @@ function radb4( ido, l1, cc, ch, wa1, wa2, wa3 ) {
 	if ( ido < 2 ) {
 		return;
 	}
-	if ( ido != 2 ) {
+	if ( ido !== 2 ) {
 		idp2 = ido + 2;
 		for ( k = 1; k <= l1; ++k ) {
 			for ( i = 3; i <= ido; i += 2 ) {

lib/node_modules/@stdlib/fft/base/fftpack/lib/radbg.js

@@ -126,7 +126,7 @@ function radbg( ido, ip, l1, idl1, cc, c1, c2, ch, ch2, wa ) {
 	// Parameter adjustments...
 	chOffset = 1 + ( ido * ( 1 + l1 ) );
 	c1Offset = 1 + ( ido * ( 1 + l1 ) );
-	ccOffset = 1 + ido * ( 1 + ip );
+	ccOffset = 1 + ( ido * ( 1 + ip ) );
 	ch2Offset = 1 + idl1;
 	c2Offset = 1 + idl1;
 

lib/node_modules/@stdlib/fft/base/fftpack/lib/radf2.js

@@ -91,7 +91,7 @@ function radf2( ido, l1, cc, ch, wa1 ) {
 
 	// Parameter adjustments...
 	chOffset = 1 + ( ido * 3 );
-	ccOffset = 1 + ido * ( 1 + l1 );
+	ccOffset = 1 + ( ido * ( 1 + l1 ) );
 
 	// Function body:
 	for ( k = 1; k <= l1; ++k ) {

lib/node_modules/@stdlib/fft/base/fftpack/lib/radf3.js

@@ -0,0 +1,149 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2024 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*
+*
+* ## Notice
+*
+* The original C code and copyright notice are from the [PFFFT library]{@link https://github.com/marton78/pffft/blob/master/fftpack.c}. The implementation follows the original, but has been modified for JavaScript.
+*
+* ```text
+* Copyright (c) 2004 the University Corporation for Atmospheric
+* Research ("UCAR"). All rights reserved. Developed by NCAR's
+* Computational and Information Systems Laboratory, UCAR,
+* www.cisl.ucar.edu.
+*
+* Redistribution and use of the Software in source and binary forms,
+* with or without modification, is permitted provided that the
+* following conditions are met:
+*
+*     - Neither the names of NCAR's Computational and Information Systems
+*       Laboratory, the University Corporation for Atmospheric Research,
+*       nor the names of its sponsors or contributors may be used to
+*       endorse or promote products derived from this Software without
+*       specific prior written permission.
+*
+*     - Redistributions of source code must retain the above copyright
+*       notices, this list of conditions, and the disclaimer below.
+*
+*     - Redistributions in binary form must reproduce the above copyright
+*       notice, this list of conditions, and the disclaimer below in the
+*       documentation and/or other materials provided with the
+*       distribution.
+*
+* THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+* EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO THE WARRANTIES OF
+* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+* NONINFRINGEMENT. IN NO EVENT SHALL THE CONTRIBUTORS OR COPYRIGHT
+* HOLDERS BE LIABLE FOR ANY CLAIM, INDIRECT, INCIDENTAL, SPECIAL,
+* EXEMPLARY, OR CONSEQUENTIAL DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE
+* SOFTWARE.
+* ```
+*/
+
+/* eslint-disable max-len */
+
+'use strict';
+
+// MODULES //
+
+var chRef = require( './ch_ref.js' );
+var ccRef = require( './cc_ref.js' );
+
+
+// VARIABLES //
+
+var taur = -0.5;
+var taui = 0.866025403784439;
+
+
+// MAIN //
+
+/**
+* Performs the forward FFT of length 3 for real-valued sequences.
+*
+* @private
+* @param {number} ido - number of real values for each transform
+* @param {number} l1 - length of the input sequences
+* @param {Float64Array} cc - input array containing sequences to be transformed
+* @param {Float64Array} ch - output array containing transformed sequences
+* @param {Float64Array} wa1 - first array of twiddle factors
+* @param {Float64Array} wa2 - second array of twiddle factors
+* @returns {void}
+*/
+function radf3( ido, l1, cc, ch, wa1, wa2 ) {
+	var chOffset;
+	var ccOffset;
+	var idp2;
+	var tr3;
+	var tr2;
+	var ti3;
+	var ti2;
+	var dr3;
+	var dr2;
+	var di3;
+	var di2;
+	var cr2;
+	var ci2;
+	var ic;
+	var i;
+	var k;
+
+	// Parameter adjustments...
+	chOffset = 1 + ( ido << 2 );
+	ccOffset = 1 + ( ido * ( 1 + l1 ) );
+
+	// Function body:
+	for ( k = 1; k <= l1; ++k ) {
+		cr2 = cc[ ccRef( 1, k, 2, l1, ido ) - ccOffset ] + cc[ ccRef( 1, k, 3, l1, ido ) - ccOffset ];
+		ch[ chRef( 1, 1, k, 3, ido ) - chOffset ] = cc[ ccRef( 1, k, 1, l1, ido ) - ccOffset ] + cr2;
+		ch[ chRef( 1, 3, k, 3, ido ) - chOffset ] = taui * ( cc[ ccRef( 1, k, 3, l1, ido ) - ccOffset ] - cc[ ccRef( 1, k, 2, l1, ido ) - ccOffset ] );
+		ch[ chRef( ido, 2, k, 3, ido ) - chOffset ] = ( cc[ ccRef( 1, k, 1, l1, ido ) - ccOffset ] + taur ) * cr2;
+	}
+	if ( ido === 1 ) {
+		return;
+	}
+	idp2 = ido + 2;
+	for ( k = 1; k <= l1; ++k ) {
+		for ( i = 3; i <= ido; i += 2 ) {
+			ic = idp2 - i;
+			dr2 = ( wa1[ i - 2 - 1 ] * cc[ ccRef( i - 1, k, 2, l1, ido ) - ccOffset ])  + ( wa1[ i - 1 - 1 ] * cc[ ccRef( i, k, 2, l1, ido ) - ccOffset ] );
+			di2 = ( wa1[ i - 2 - 1 ] * cc[ ccRef( i, k, 2, l1, ido ) - ccOffset ])  - ( wa1[ i - 1 - 1 ] * cc[ ccRef( i - 1, k, 2, l1, ido ) - ccOffset ] );
+			dr3 = ( wa2[ i - 2 - 1 ] * cc[ ccRef( i - 1, k, 3, l1, ido ) - ccOffset ])  + ( wa2[ i - 1 - 1 ] * cc[ ccRef( i, k, 3, l1, ido ) - ccOffset ] );
+			di3 = ( wa2[ i - 2 - 1 ] * cc[ ccRef( i, k, 3, l1, ido ) - ccOffset ])  - ( wa2[ i - 1 - 1 ] * cc[ ccRef( i - 1, k, 3, l1, ido ) - ccOffset ] );
+			cr2 = dr2 + dr3;
+			ci2 = di2 + di3;
+			ch[ chRef( i - 1, 1, k, 3, ido ) - chOffset ] = cc[ ccRef( i - 1, k, 1, l1, ido ) - ccOffset ] + cr2;
+			ch[ chRef( i, 1, k, 3, ido ) - chOffset ] = cc[ ccRef( i, k, 1, l1, ido ) - ccOffset ] + ci2;
+			tr2 = cc[ ccRef( i - 1, k, 1, l1, ido ) - ccOffset ] + ( taur * cr2 );
+			ti2 = cc[ ccRef( i, k, 1, l1, ido ) - ccOffset ] + ( taur * ci2 );
+			tr3 = taui * ( di2 - di3 );
+			ti3 = taui * ( dr3 - dr2 );
+			ch[ chRef( i - 1, 3, k, 3, ido ) - chOffset ] = tr2 + tr3;
+			ch[ chRef( ic - 1, 2, k, 3, ido ) - chOffset ] = tr2 - tr3;
+			ch[ chRef( i, 3, k, 3, ido ) - chOffset ] = ti2 + ti3;
+			ch[ chRef( ic, 2, k, 3, ido ) - chOffset ] = ti3 - ti2;
+		}
+	}
+
+}
+
+
+// EXPORTS //
+
+module.exports = radf3;