Press n or j to go to the next uncovered block, b, p or k for the previous block.
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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';
// MODULES //
var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
var cospi = require( '@stdlib/math/base/special/cospi' );
var accessors = require( './accessors.js' );
// VARIABLES //
var M = 5;
// MAIN //
/**
* Generates a cosine wave in a strided array.
*
* @param {PositiveInteger} N - number of indexed elements
* @param {PositiveInteger} period - period (i.e., the number of elements before a cosine wave repeats)
* @param {NonNegativeNumber} amplitude - peak amplitude
* @param {integer} phaseOffset - phase offset (in units of elements; zero-based). A negative offset translates a waveform to the left. A positive offset translates a waveform to the right
* @param {NumericArray} x - input array
* @param {integer} strideX - stride length
* @param {NonNegativeInteger} offsetX - starting index
* @returns {NumericArray} input array
*
* @example
* var x = [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ];
*
* cosineWave( x.length, 4, 1.0, 0, x, 1, 0 );
* // x => [ 1.0, 0.0, -1.0, 0.0, 1.0, 0.0 ]
*/
function cosineWave( N, period, amplitude, phaseOffset, x, strideX, offsetX ) {
var theta;
var ix;
var m;
var s;
var o;
var i;
if ( N <= 0 || amplitude < 0.0 || period <= 0 ) {
return x;
}
o = arraylike2object( x );
if ( o.accessorProtocol ) {
return accessors( N, period, amplitude, phaseOffset, o, strideX, offsetX ); // eslint-disable-line max-len
}
ix = offsetX;
theta = -phaseOffset;
s = 2.0 / period;
// Use loop unrolling if the stride is equal to `1`...
if ( strideX === 1 ) {
m = N % M;
// If we have a remainder, run a clean-up loop...
if ( m > 0 ) {
for ( i = 0; i < m; i++ ) {
x[ ix ] = amplitude * cospi( s * theta );
theta += 1.0;
ix += strideX;
}
}
if ( N < M ) {
return x;
}
for ( i = m; i < N; i += M ) {
x[ ix ] = amplitude * cospi( s * theta );
theta += 1.0;
x[ ix+1 ] = amplitude * cospi( s * theta );
theta += 1.0;
x[ ix+2 ] = amplitude * cospi( s * theta );
theta += 1.0;
x[ ix+3 ] = amplitude * cospi( s * theta );
theta += 1.0;
x[ ix+4 ] = amplitude * cospi( s * theta );
theta += 1.0;
ix += M;
}
return x;
}
for ( i = 0; i < N; i++ ) {
x[ ix ] = amplitude * cospi( s * theta );
theta += 1.0;
ix += strideX;
}
return x;
}
// EXPORTS //
module.exports = cosineWave;
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