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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.
*/
'use strict';
/* eslint-disable vars-on-top */
// MODULES //
var dtypes = require( '@stdlib/ndarray/dtypes' );
var factory = require( '@stdlib/ndarray/base/nullary-strided1d-dispatch-factory' );
var isEven = require( '@stdlib/math/base/assert/is-even' );
var floor = require( '@stdlib/math/base/special/floor' );
var numelDimension = require( '@stdlib/ndarray/base/numel-dimension' );
var getStride = require( '@stdlib/ndarray/base/stride' );
var getOffset = require( '@stdlib/ndarray/base/offset' );
var getData = require( '@stdlib/ndarray/base/data-buffer' );
var gcopy = require( '@stdlib/blas/base/gcopy' ).ndarray;
var reinterpret = require( '@stdlib/strided/base/reinterpret-complex' );
var reinterpret128 = require( '@stdlib/strided/base/reinterpret-complex128' );
var reinterpret64 = require( '@stdlib/strided/base/reinterpret-complex64' );
var Float64Array = require( '@stdlib/array/float64' );
var Float32Array = require( '@stdlib/array/float32' );
var drffti = require( '@stdlib/fft/base/fftpack/float64/rffti' );
var drfftf = require( '@stdlib/fft/base/fftpack/float64/rfftf' );
var srffti = require( '@stdlib/fft/base/fftpack/float32/rffti' );
var srfftf = require( '@stdlib/fft/base/fftpack/float32/rfftf' );
var grffti = require( '@stdlib/fft/base/fftpack/generic/rffti' );
var grfftf = require( '@stdlib/fft/base/fftpack/generic/rfftf' );
// FUNCTIONS //
/**
* Computes the forward FFT and writes results to the output complex ndarray.
*
* @private
* @param {Function} reinterpret - complex-to-real reinterpret function
* @param {Function} rffti - workspace initialization function
* @param {Function} rfftf - forward FFT function
* @param {Function} Workspace - typed array constructor for workspace
* @param {ArrayLikeObject<Object>} arrays - array-like object containing ndarrays
* @returns {void}
*/
function kernel( reinterpret, rffti, rfftf, Workspace, arrays ) {
var view;
var out;
var M;
var N;
var w;
var x;
out = arrays[ 0 ];
x = arrays[ 1 ];
N = numelDimension( x, 0 );
M = floor( N/2 ) + 1;
view = reinterpret( getData( out ), 0 );
if ( N === 0 ) {
return;
}
// Copy the input into the output buffer at offset 1:
gcopy( N, getData( x ), getStride( x, 0 ), getOffset( x ), view, 1, 1 );
// Initialize the workspace and compute the forward FFT in-place:
w = new Workspace( ( 2*N ) + 34 );
rffti( N, w, 1, 0 );
rfftf( N, view, 1, 1, w, 1, 0 );
// Move the DC component from the imaginary slot to the real slot of the first complex element and zero out the imaginary part:
view[ 0 ] = view[ 1 ];
view[ 1 ] = 0.0;
// For even-length sequences, zero out the imaginary part of the Nyquist component:
if ( isEven( N ) ) {
view[ ( 2*M ) - 1 ] = 0.0;
}
}
/**
* Computes the forward FFT of a real-valued input.
*
* @private
* @param {ArrayLikeObject<Object>} arrays - array-like object containing ndarrays
* @returns {void}
*/
function gkernel( arrays ) {
kernel( reinterpret, grffti, grfftf, Float64Array, arrays );
}
/**
* Computes the forward FFT of a real-valued double-precision input.
*
* @private
* @param {ArrayLikeObject<Object>} arrays - array-like object containing ndarrays
* @returns {void}
*/
function dkernel( arrays ) {
kernel( reinterpret128, drffti, drfftf, Float64Array, arrays );
}
/**
* Computes the forward FFT of a real-valued single-precision input.
*
* @private
* @param {ArrayLikeObject<Object>} arrays - array-like object containing ndarrays
* @returns {void}
*/
function skernel( arrays ) {
kernel( reinterpret64, srffti, srfftf, Float32Array, arrays );
}
// VARIABLES //
var idtypes = dtypes( 'real_and_generic' );
var odtypes = dtypes( 'complex_floating_point' );
var table = {
'types': [
'complex128',
'complex64'
],
'fcns': [
dkernel,
skernel
],
'default': gkernel
};
// MAIN //
/**
* Computes the one-dimensional discrete Fourier transform of a real-valued input ndarray and assigns the results to a provided output ndarray.
*
* @private
* @name rfftf
* @type {Function}
* @param {ndarray} out - output ndarray
* @param {ndarray} x - input ndarray
* @throws {TypeError} first argument must be an ndarray-like object
* @throws {TypeError} second argument must be an ndarray-like object
* @returns {ndarray} output ndarray
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var Complex128Array = require( '@stdlib/array/complex128' );
* var ndarray = require( '@stdlib/ndarray/ctor' );
*
* // Create a data buffer:
* var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
*
* // Define the shape of the input array:
* var sh = [ 4 ];
*
* // Define the array strides:
* var sx = [ 1 ];
*
* // Define the index offset:
* var ox = 0;
*
* // Create an input ndarray:
* var x = new ndarray( 'float64', xbuf, sh, sx, ox, 'row-major' );
*
* // Create an output ndarray:
* var out = new ndarray( 'complex128', new Complex128Array( 3 ), [ 3 ], [ 1 ], 0, 'row-major' );
*
* // Perform operation:
* var v = rfftf( out, x );
* // returns <ndarray>[ <Complex128>[ 10.0, 0.0 ], <Complex128>[ -2.0, 2.0 ], <Complex128>[ -2.0, 0.0 ] ]
*/
var rfftf = factory( table, [ idtypes ], odtypes );
// EXPORTS //
module.exports = rfftf;
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