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* @license Apache-2.0
*
* Copyright (c) 2019 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 setReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
var iteratorSymbol = require( '@stdlib/symbol/iterator' );
var cospi = require( '@stdlib/math/base/special/cospi' );
var validate = require( './validate.js' );
// MAIN //
/**
* Returns an iterator which generates a cosine wave.
*
* @param {Options} [options] - function options
* @param {PositiveInteger} [options.period=10] - number of iterations before a cosine wave repeats
* @param {NonNegativeNumber} [options.amplitude=1.0] - peak amplitude
* @param {integer} [options.offset=0] - phase offset (in units of iterations; zero-based)
* @param {NonNegativeInteger} [options.iter=1e308] - number of iterations
* @throws {TypeError} options argument must be an object
* @throws {TypeError} must provide valid options
* @returns {Iterator} iterator
*
* @example
* var opts = {
* 'period': 4
* };
*
* var iter = iterCosineWave( opts );
*
* var v = iter.next().value;
* // returns 1.0
*
* v = iter.next().value;
* // returns 0.0
*
* v = iter.next().value;
* // returns -1.0
*
* // ...
*/
function iterCosineWave( options ) {
var opts;
var iter;
var FLG;
var err;
var t;
var s;
var i;
opts = {
'period': 10,
'amplitude': 1.0,
'offset': 0,
'iter': 1e308
};
if ( arguments.length ) {
err = validate( opts, options );
if ( err ) {
throw err;
}
}
t = ( opts.period-opts.offset ) % opts.period;
if ( t < 0 ) {
t += opts.period; // normalize such that t ϵ [0,τ]
}
t -= 1;
s = 2.0 / opts.period;
i = 0;
// Create an iterator protocol-compliant object:
iter = {};
setReadOnly( iter, 'next', next );
setReadOnly( iter, 'return', end );
// If an environment supports `Symbol.iterator`, make the iterator iterable:
if ( iteratorSymbol ) {
setReadOnly( iter, iteratorSymbol, factory );
}
return iter;
/**
* Returns an iterator protocol-compliant object containing the next iterated value.
*
* @private
* @returns {Object} iterator protocol-compliant object
*/
function next() {
i += 1;
if ( FLG || i > opts.iter ) {
return {
'done': true
};
}
t += 1;
t %= opts.period;
return {
'value': opts.amplitude * cospi( s*t ),
'done': false
};
}
/**
* Finishes an iterator.
*
* @private
* @param {*} [value] - value to return
* @returns {Object} iterator protocol-compliant object
*/
function end( value ) {
FLG = true;
if ( arguments.length ) {
return {
'value': value,
'done': true
};
}
return {
'done': true
};
}
/**
* Returns a new iterator.
*
* @private
* @returns {Iterator} iterator
*/
function factory() {
return iterCosineWave( opts );
}
}
// EXPORTS //
module.exports = iterCosineWave;
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