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* @license Apache-2.0
*
* Copyright (c) 2026 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/0b4ee12c4ba45a4a8e567550c16d96d1679f50ce/src/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.
* ```
*/
'use strict';
// MODULES //
var rfftf1 = require( './rfftf1.js' );
// MAIN //
/**
* Computes the forward discrete Fourier transform (DFT) of a real-valued sequence.
*
* @param {NonNegativeInteger} N - length of the sequence to transform
* @param {Collection} r - input array
* @param {integer} strideR - stride length for `r`
* @param {NonNegativeInteger} offsetR - starting index for `r`
* @param {Collection} w - workspace array containing pre-computed values
* @param {integer} strideW - stride length for `w`
* @param {NonNegativeInteger} offsetW - starting index for `w`
* @returns {Collection} input array
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var rffti = require( '@stdlib/fft/base/fftpack/generic/rffti' );
*
* var N = 4;
*
* var w = new Float64Array( ( 2*N ) + 34 );
* rffti( N, w, 1, 0 );
*
* var r = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
*
* rfftf( N, r, 1, 0, w, 1, 0 );
* // r => <Float64Array>[ 10.0, -2.0, 2.0, -2.0 ]
*/
function rfftf( N, r, strideR, offsetR, w, strideW, offsetW ) {
var offsetT;
var offsetF;
// When a sub-sequence is a single data point, the FFT is the identity, so no transformation necessary...
if ( N === 1 ) {
return r;
}
// Resolve the starting indices for storing twiddle factors and factorization results:
offsetT = offsetW + ( N * strideW ); // index offset for twiddle factors
offsetF = offsetT + ( N * strideW ); // index offset for factors describing the sub-transforms
rfftf1( N, r, strideR, offsetR, w, strideW, offsetW, w, strideW, offsetT, w, strideW, offsetF ); // eslint-disable-line max-len
return r;
}
// EXPORTS //
module.exports = rfftf;
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