feat: add fft/base/fftpack/rfftf

lib/node_modules/@stdlib/fft/base/fftpack/rfftf/lib/index.js

@@ -0,0 +1,49 @@
+/**
+* @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.
+*/
+
+'use strict';
+
+/**
+* Compute the forward real-valued fast Fourier transform (FFT).
+*
+* @module @stdlib/fft/base/fftpack/rfftf
+*
+* @example
+* var Float64Array = require( '@stdlib/array/float64' );
+* var rffti = require( '@stdlib/fft/base/fftpack/rffti' );
+* var rfftf = require( '@stdlib/fft/base/fftpack/rfftf' );
+*
+* var N = 4;
+*
+* var workspace = new Float64Array( ( 2*N ) + 34 );
+* rffti( N, workspace, 1, 0 );
+*
+* var r = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
+*
+* rfftf( N, r, 1, 0, workspace, 1, 0 );
+* // r => <Float64Array>[ 10.0, -2.0, 2.0, -2.0 ]
+*/
+
+// MODULES //
+
+var main = require( './main.js' );
+
+
+// EXPORTS //
+
+module.exports = main;

lib/node_modules/@stdlib/fft/base/fftpack/rfftf/lib/main.js

@@ -0,0 +1,124 @@
+/**
+* @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/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.
+* ```
+*/
+
+'use strict';
+
+// MODULES //
+
+var isNonNegativeInteger = require( '@stdlib/assert/is-nonnegative-integer' );
+var isFloat64Array = require( '@stdlib/assert/is-float64array' );
+var isInteger = require( '@stdlib/assert/is-integer' );
+var rfftf1 = require( './rfftf1.js' );
+
+
+// MAIN //
+
+/**
+* Computes the forward real-valued fast Fourier transform (FFT).
+*
+* @param {NonNegativeInteger} N - length of the sequence to transform
+* @param {Float64Array} r - input array containing the sequence to transform
+* @param {integer} strideR - stride length for `r`
+* @param {NonNegativeInteger} offsetR - starting index for `r`
+* @param {Float64Array} workspace - workspace array containing pre-computed values
+* @param {integer} strideW - stride length for `workspace`
+* @param {NonNegativeInteger} offsetW - starting index for `workspace`
+* @returns {void}
+*
+* @example
+* var Float64Array = require( '@stdlib/array/float64' );
+* var rffti = require( '@stdlib/fft/base/fftpack/rffti' );
+*
+* var N = 4;
+*
+* var workspace = new Float64Array( ( 2*N ) + 34 );
+* rffti( N, workspace, 1, 0 );
+*
+* var r = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
+*
+* rfftf( N, r, 1, 0, workspace, 1, 0 );
+* // r => <Float64Array>[ 10.0, -2.0, 2.0, -2.0 ]
+*/
+function rfftf( N, r, strideR, offsetR, workspace, strideW, offsetW ) {
+	var offsetT;
+	var offsetF;
+
+	if ( !isNonNegativeInteger( N ) || !isFloat64Array( r ) ||
+		!isInteger( strideR ) || !isNonNegativeInteger( offsetR ) ||
+		!isFloat64Array( workspace ) || !isInteger( strideW ) ||
+		!isNonNegativeInteger( offsetW ) ||
+		workspace.length < offsetW + ( ( ( 2*N ) + 34 ) * strideW ) ) {
+		return;
+	}
+
+	// When a sub-sequence is a single data point, the FFT is the identity, so no transformation necessary...
+	if ( N === 1 ) {
+		return;
+	}
+
+	// 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, offsetR, workspace, offsetW, workspace, offsetT, workspace, offsetF ); // eslint-disable-line max-len
+}
+
+
+// EXPORTS //
+
+module.exports = rfftf;