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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 floor = require( '@stdlib/math/base/special/floor' );
var radf2 = require( './radf2.js' );
var radf3 = require( './radf3.js' );
var radf4 = require( './radf4.js' );
var radf5 = require( './radf5.js' );
var radfg = require( './radfg.js' );
var printWorkspace = require( './print_real_workspace.js' ); // FIXME
// MAIN //
/**
* Performs the forward real-valued Fourier transform.
*
* @private
* @param {NonNegativeInteger} N - length of the sequence to transform
* @param {Float64Array} c - input array containing the sequence to be transformed
* @param {NonNegativeInteger} cOffset - starting index for `c`
* @param {Float64Array} ch - working array for intermediate results
* @param {NonNegativeInteger} chOffset - starting index for `ch`
* @param {Float64Array} wa - workspace array for storing twiddle factors
* @param {NonNegativeInteger} waOffset - starting index for `wa`
* @param {Int32Array} ifac - workspace array for storing factorization results
* @param {NonNegativeInteger} ifacOffset - starting index for `ifac`
* @returns {void}
*/
function rfftf1( N, c, cOffset, ch, chOffset, wa, waOffset, ifac, ifacOffset ) {
var factor;
var idl1;
var FLG;
var ido;
var ix4;
var ix3;
var ix2;
var nf;
var l2;
var l1;
var kh;
var iw;
var k1;
var i;
// Resolve the number of factors:
nf = ifac[ ifacOffset+1 ];
FLG = 1; // FIXME: describe the point of this flag
l2 = N;
// FIXME
printWorkspace( N, ch, 1, chOffset );
// Initialize an index offset to the last element in each workspace:
iw = N - 1;
for ( k1 = 1; k1 <= nf; k1++ ) {
kh = nf - k1;
// Resolve the next factor:
factor = ifac[ ifacOffset+kh+2 ];
// Compute a sub-transform length:
l1 = floor( l2 / factor );
ido = floor( N / l2 );
idl1 = ido * l1;
// Adjust the index offset
iw -= ( (factor-1) * ido );
// Toggle the flag: // FIXME: better description?
FLG = 1 - FLG;
switch ( factor ) {
case 4:
ix2 = iw + ido;
ix3 = ix2 + ido;
radf4( ido, l1, ( FLG ) ? ch : c, ( FLG ) ? chOffset : cOffset, ( FLG ) ? c : ch, ( FLG ) ? cOffset : chOffset, wa, iw+waOffset, wa, ix2+waOffset, wa, ix3+waOffset );
break;
case 2:
radf2( ido, l1, ( FLG ) ? ch : c, 1, ( FLG ) ? chOffset : cOffset, ( FLG ) ? c : ch, 1, ( FLG ) ? cOffset : chOffset, wa, 1, iw+waOffset );
break;
case 3:
ix2 = iw + ido;
radf3( ido, l1, ( FLG ) ? ch : c, ( FLG ) ? chOffset : cOffset, ( FLG ) ? c : ch, ( FLG ) ? cOffset : chOffset, wa, iw+waOffset, wa, ix2+waOffset );
break;
case 5:
ix2 = iw + ido;
ix3 = ix2 + ido;
ix4 = ix3 + ido;
radf5( ido, l1, ( FLG ) ? ch : c, ( FLG ) ? chOffset : cOffset, ( FLG ) ? c : ch, ( FLG ) ? cOffset : chOffset, wa, iw+waOffset, wa, ix2+waOffset, wa, ix3+waOffset, wa, ix4+waOffset );
break;
default:
if ( ido === 1 ) {
FLG = 1 - FLG;
}
if ( FLG === 0 ) {
radfg( ido, factor, l1, idl1, c, cOffset, c, cOffset, c, cOffset, ch, chOffset, ch, chOffset, wa, iw+waOffset );
FLG = 1;
} else {
radfg( ido, factor, l1, idl1, ch, chOffset, ch, chOffset, ch, chOffset, c, cOffset, c, cOffset, wa, iw+waOffset );
FLG = 0;
}
break;
}
l2 = l1;
}
if ( FLG === 1 ) {
return;
}
// Now that we've finished computing the transforms, copy over the final results to the input array...
for ( i = 0; i < N; i++ ) {
c[ cOffset+i ] = ch[ chOffset+i ]; // FIXME: use `blas/base/dcopy`
}
}
// EXPORTS //
module.exports = rfftf1;
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