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* @license Apache-2.0
*
* Copyright (c) 2025 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 SQRT2 = require( '@stdlib/constants/float64/sqrt-two' );
var chRef = require( './ch_ref.js' );
var ccRef = require( './cc_ref.js' );
// MAIN //
/**
* Performs the backward FFT of length 4 for real-valued sequences.
*
* @private
* @param {integer} ido - number of real values for each transform
* @param {integer} l1 - length of the input sequences
* @param {Float64Array} cc - input array containing sequences to be transformed
* @param {number} ccOffset - offset for the input array
* @param {Float64Array} ch - output array containing transformed sequences
* @param {number} chOffset - offset for the output array
* @param {Float64Array} wa1 - first array of twiddle factors
* @param {number} wa1Offset - offset for the first twiddle factors array
* @param {Float64Array} wa2 - second array of twiddle factors
* @param {number} wa2Offset - offset for the second twiddle factors array
* @param {Float64Array} wa3 - third array of twiddle factors
* @param {number} wa3Offset - offset for the third twiddle factors array
* @returns {void}
*/
function radb4( ido, l1, cc, ccOffset, ch, chOffset, wa1, wa1Offset, wa2, wa2Offset, wa3, wa3Offset ) { // eslint-disable-line max-params
var idp2;
var ti1;
var ti2;
var ti3;
var ti4;
var tr1;
var tr2;
var tr3;
var tr4;
var ci2;
var ci3;
var ci4;
var cr2;
var cr3;
var cr4;
var ic;
var i;
var k;
// Parameter adjustments...
chOffset -= 1 + ( ido * ( 1 + l1 ) );
ccOffset -= 1 + ( ido * 5 );
wa1Offset -= 1;
wa2Offset -= 1;
wa3Offset -= 1;
// Function body:
for ( k = 1; k <= l1; k++ ) {
tr1 = cc[ ccRef( 1, 1, k, 4, ido ) + ccOffset ] - cc[ ccRef( ido, 4, k, 4, ido ) + ccOffset ];
tr2 = cc[ ccRef( 1, 1, k, 4, ido ) + ccOffset ] + cc[ ccRef( ido, 4, k, 4, ido ) + ccOffset ];
tr3 = cc[ ccRef( ido, 2, k, 4, ido ) + ccOffset ] + cc[ ccRef( ido, 2, k, 4, ido ) + ccOffset ];
tr4 = cc[ ccRef( 1, 3, k, 4, ido ) + ccOffset ] + cc[ ccRef( 1, 3, k, 4, ido ) + ccOffset ];
ch[ chRef( 1, k, 1, l1, ido ) + chOffset ] = tr2 + tr3;
ch[ chRef( 1, k, 2, l1, ido ) + chOffset ] = tr1 - tr4;
ch[ chRef( 1, k, 3, l1, ido ) + chOffset ] = tr2 - tr3;
ch[ chRef( 1, k, 4, l1, ido ) + chOffset ] = tr1 + tr4;
}
if ( ido < 2 ) {
return;
}
if ( ido !== 2 ) {
idp2 = ido + 2;
for ( k = 1; k <= l1; k++ ) {
for ( i = 3; i <= ido; i += 2 ) {
ic = idp2 - i;
ti1 = cc[ ccRef( i, 1, k, 4, ido ) + ccOffset ] + cc[ ccRef( ic, 4, k, 4, ido ) + ccOffset ];
ti2 = cc[ ccRef( i, 1, k, 4, ido ) + ccOffset ] - cc[ ccRef( ic, 4, k, 4, ido ) + ccOffset ];
ti3 = cc[ ccRef( i, 3, k, 4, ido ) + ccOffset ] - cc[ ccRef( ic, 2, k, 4, ido ) + ccOffset ];
ti4 = cc[ ccRef( i, 3, k, 4, ido ) + ccOffset ] + cc[ ccRef( ic, 2, k, 4, ido ) + ccOffset ];
tr1 = cc[ ccRef( i - 1, 1, k, 4, ido ) + ccOffset ] - cc[ ccRef( ic - 1, 4, k, 4, ido ) + ccOffset ];
tr2 = cc[ ccRef( i - 1, 1, k, 4, ido ) + ccOffset ] + cc[ ccRef( ic - 1, 4, k, 4, ido ) + ccOffset ];
ti4 = cc[ ccRef( i - 1, 3, k, 4, ido ) + ccOffset ] - cc[ ccRef( ic - 1, 2, k, 4, ido ) + ccOffset ];
tr3 = cc[ ccRef( i - 1, 3, k, 4, ido ) + ccOffset ] + cc[ ccRef( ic - 1, 2, k, 4, ido ) + ccOffset ];
ch[ chRef( i - 1, k, 1, l1, ido ) + chOffset ] = tr2 + tr3;
cr3 = tr2 - tr3;
ch[ chRef( i, k, 1, l1, ido ) + chOffset ] = ti2 + ti3;
ci3 = ti2 - ti3;
cr2 = tr1 - tr4;
cr4 = tr1 + tr4;
ci2 = ti1 + ti4;
ci4 = ti1 - ti4;
ch[ chRef( i - 1, k, 2, l1, ido ) + chOffset ] = ( wa1[ i - 2 + wa1Offset ] * cr2 ) - ( wa1[ i - 1 + wa1Offset ] * ci2 );
ch[ chRef( i, k, 2, l1, ido ) + chOffset ] = ( wa1[ i - 2 + wa1Offset ] * ci2 ) + ( wa1[ i - 1 + wa1Offset ] * cr2 );
ch[ chRef( i - 1, k, 3, l1, ido ) + chOffset ] = ( wa2[ i - 2 + wa2Offset ] * cr3 ) - ( wa2[ i - 1 + wa2Offset ] * ci3 );
ch[ chRef( i, k, 3, l1, ido ) + chOffset ] = ( wa2[ i - 2 + wa2Offset ] * ci3 ) + ( wa2[ i - 1 + wa2Offset ] * cr3 );
ch[ chRef( i - 1, k, 4, l1, ido ) + chOffset ] = ( wa3[ i - 2 + wa3Offset ] * cr4 ) - ( wa3[ i - 1 + wa3Offset ] * ci4 );
ch[ chRef( i, k, 4, l1, ido ) + chOffset ] = ( wa3[ i - 2 + wa3Offset ] * ci4 ) + ( wa3[ i - 1 + wa3Offset ] * cr4 );
}
}
if ( ido % 2 === 1 ) {
return;
}
}
for ( k = 1; k <= l1; k++ ) {
ti1 = cc[ ccRef( 1, 2, k, 4, ido ) + ccOffset ] + cc[ ccRef( 1, 4, k, 4, ido ) + ccOffset ];
ti2 = cc[ ccRef( 1, 4, k, 4, ido ) + ccOffset ] - cc[ ccRef( 1, 2, k, 4, ido ) + ccOffset ];
tr1 = cc[ ccRef( ido, 1, k, 4, ido ) + ccOffset ] - cc[ ccRef( ido, 3, k, 4, ido ) + ccOffset ];
tr2 = cc[ ccRef( ido, 1, k, 4, ido ) + ccOffset ] + cc[ ccRef( ido, 3, k, 4, ido ) + ccOffset ];
ch[ chRef( ido, k, 1, l1, ido ) + chOffset ] = tr2 + tr2;
ch[ chRef( ido, k, 2, l1, ido ) + chOffset ] = SQRT2 * ( tr1 - ti1 );
ch[ chRef( ido, k, 3, l1, ido ) + chOffset ] = ti2 + ti2;
ch[ chRef( ido, k, 4, l1, ido ) + chOffset ] = -SQRT2 * ( tr1 + ti1 );
}
}
// EXPORTS //
module.exports = radb4;
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