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* @license Apache-2.0
*
* Copyright (c) 2020 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 validate = require( './validate.js' );
// VARIABLES //
var L0 = 2;
var L1 = 1;
// MAIN //
/**
* Returns an iterator which generates a Lucas sequence.
*
* ## Notes
*
* - The returned iterator can only generate the first `77` Lucas numbers, as larger Lucas numbers cannot be safely represented in double-precision floating-point format.
* - If an environment supports `Symbol.iterator`, the returned iterator is iterable.
*
* @param {Options} [options] - function options
* @param {NonNegativeInteger} [options.iter=77] - number of iterations
* @throws {TypeError} options argument must be an object
* @throws {TypeError} must provide valid options
* @throws {RangeError} `iter` option must be less than or equal to `77`
* @returns {Iterator} iterator
*
* @example
* var iter = iterLucasSeq();
*
* var v = iter.next().value;
* // returns 2
*
* v = iter.next().value;
* // returns 1
*
* v = iter.next().value;
* // returns 3
*
* // ...
*/
function iterLucasSeq( options ) {
var opts;
var iter;
var FLG;
var err;
var l1;
var l2;
var l;
var i;
opts = {
'iter': 77
};
if ( arguments.length ) {
err = validate( opts, options );
if ( err ) {
throw err;
}
}
l1 = L0;
l2 = L1;
l = 0;
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
};
}
if ( i === 1 ) {
l = L0;
} else if ( i === 2 ) {
l = L1;
} else {
l = l1 + l2;
l1 = l2;
l2 = l;
}
return {
'value': l,
'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 iterLucasSeq( opts );
}
}
// EXPORTS //
module.exports = iterLucasSeq;
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