text: /**
  * @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 setReadOnlyAccessor = require( '@stdlib/utils/define-nonenumerable-read-only-accessor' );
  var setReadWriteAccessor = require( '@stdlib/utils/define-nonenumerable-read-write-accessor' );
  var isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
  var isPositiveNumber = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
  var isPlainObject = require( '@stdlib/assert/is-plain-object' );
  var isFunction = require( '@stdlib/assert/is-function' );
  var isBoolean = require( '@stdlib/assert/is-boolean' ).isPrimitive;
  var isUint32Array = require( '@stdlib/assert/is-uint32array' );
  var hasOwnProp = require( '@stdlib/assert/has-own-property' );
  var copy = require( '@stdlib/utils/copy' );
  var noop = require( '@stdlib/utils/noop' );
  var constantFunction = require( '@stdlib/utils/constant-function' );
  var iteratorSymbol = require( '@stdlib/symbol/iterator' );
  var randu = require( '@stdlib/random/base/uniform' ).factory;
  var SQRT_THREE = require( '@stdlib/constants/math/float64-sqrt-three' );
  var DEFAULTS = require( './defaults.json' );
  
  
  // MAIN //
  
  /**
  * Returns an iterator which introduces additive white uniform noise with standard deviation `sigma`.
  *
  * ## Method
  *
  * -   The variance of a uniform distribution is given by
  *
  *     ```tex
  *     \operatorname{Var} = \frac{(b-a)^2}{12}
  *     ```
  *
  *     where \\( a \\) is the minimum support and \\( b \\) is the maximum support.
  *
  * -   Accordingly, to generate uniform noise having zero mean and a desired standard deviation, we let \\( a = -b \\) and solve for \\( b \\).
  *
  *     ```tex
  *     \begin{align*}
  *     \sigma &= \frac{b-a}{\sqrt{12}} \\
  *     \sigma \sqrt{12} &= b - a \\
  *     2 \sigma \sqrt{3} &= b - (-b) \\
  *     2 \sigma \sqrt{3} &= 2b \\
  *     b &= \sigma \sqrt{3}
  *     \end{align*}
  *     ```
  *
  *     where \\( \sigma \\) is the standard deviation.
  *
  * -   Thus, to generate uniform noise having zero mean and a desired standard deviation, we sample from \\( \operatorname{unif}(-sigma\sqrt{3}, sigma\sqrt{3}) \\).
  *
  * @param {Iterator} iterator - input iterator
  * @param {PositiveNumber} sigma - standard deviation of the noise
  * @param {Options} [options] - function options
  * @param {PRNG} [options.prng] - pseudorandom number generator which generates uniformly distributed pseudorandom numbers on the interval `[0,1)`
  * @param {PRNGSeedMT19937} [options.seed] - pseudorandom number generator seed
  * @param {PRNGStateMT19937} [options.state] - pseudorandom number generator state
  * @param {boolean} [options.copy=true] - boolean indicating whether to copy a provided pseudorandom number generator state
  * @throws {TypeError} first argument must be an iterator
  * @throws {TypeError} second argument must be a positive number
  * @throws {TypeError} third argument must be an object
  * @throws {TypeError} must provide valid options
  * @throws {Error} must provide a valid state
  * @returns {Iterator} iterator
  *
  * @example
  * var iterSineWave = require( '@stdlib/simulate/iter/sine-wave' );
  *
  * var sine = iterSineWave({
  *     'iter': 100
  * });
  *
  * var it = iterawun( sine, 0.5 );
  *
  * var v = it.next().value;
  * // returns <number>
  *
  * v = it.next().value;
  * // returns <number>
  *
  * v = it.next().value;
  * // returns <number>
  *
  * // ...
  */
  function iterawun( iterator, sigma, options ) {
  	var runif;
  	var opts;
  	var iter;
  	var FLG;
  	var a;
  	if ( !isIteratorLike( iterator ) ) {
  		throw new TypeError( 'invalid argument. First argument must be an iterator. Value: `' + iterator + '`.' );
  	}
  	if ( !isPositiveNumber( sigma ) ) {
  		throw new TypeError( 'invalid argument. Second argument must be a positive number. Value: `' + sigma + '`.' );
  	}
  	opts = copy( DEFAULTS );
  	if ( arguments.length > 2 ) {
  		if ( !isPlainObject( options ) ) {
  			throw new TypeError( 'invalid argument. Third argument must be an object. Value: `' + options + '`.' );
  		}
  		if ( hasOwnProp( options, 'copy' ) ) {
  			opts.copy = options.copy;
  			if ( !isBoolean( options.copy ) ) {
  				throw new TypeError( 'invalid option. `copy` option must be a boolean. Option: `' + options.copy + '`.' );
  			}
  		}
  		if ( hasOwnProp( options, 'prng' ) ) {
  			if ( !isFunction( options.prng ) ) {
  				throw new TypeError( 'invalid option. `prng` option must be a pseudorandom number generator function. Option: `' + options.prng + '`.' );
  			}
  			opts.prng = options.prng;
  		}
  		// If provided a PRNG, ignore the `state` option, as we don't support getting or setting PRNG state.
  		else if ( hasOwnProp( options, 'state' ) ) {
  			opts.state = options.state;
  			if ( !isUint32Array( options.state ) ) {
  				throw new TypeError( 'invalid option. `state` option must be a Uint32Array. Option: `' + options.state + '`.' );
  			}
  		}
  		// If provided a PRNG, ignore the `seed` option, as a `seed`, by itself, is insufficient to guarantee reproducibility. If provided a state, ignore the `seed` option, as a PRNG state should contain seed information.
  		else if ( hasOwnProp( options, 'seed' ) ) {
  			opts.seed = options.seed;
  			if ( options.seed === void 0 ) {
  				throw new TypeError( 'invalid option. `seed` option must be either a positive integer less than or equal to the maximum unsigned 32-bit integer or an array-like object containing integer values less than or equal to the maximum unsigned 32-bit integer. Option: `' + options.seed + '`.' );
  			}
  		}
  	}
  	a = sigma * SQRT_THREE;
  	runif = randu( -a, a, opts );
  
  	// Create an iterator protocol-compliant object:
  	iter = {};
  	setReadOnly( iter, 'next', next );
  	setReadOnly( iter, 'return', end );
  
  	// If an environment supports `Symbol.iterator` and the provided iterator is iterable, make the iterator iterable:
  	if ( iteratorSymbol && isFunction( iterator[ iteratorSymbol ] ) ) {
  		setReadOnly( iter, iteratorSymbol, factory );
  	}
  	// If we are provided an "external" PRNG, we don't support getting or setting PRNG state, as we'd need to check for compatible state value types, etc, entailing considerable complexity.
  	if ( options && options.prng ) {
  		setReadOnly( iter, 'seed', null );
  		setReadOnly( iter, 'seedLength', null );
  		setReadWriteAccessor( iter, 'state', constantFunction( null ), noop );
  		setReadOnly( iter, 'stateLength', null );
  		setReadOnly( iter, 'byteLength', null );
  		setReadOnly( iter, 'PRNG', options.prng );
  	} else {
  		setReadOnlyAccessor( iter, 'seed', getSeed );
  		setReadOnlyAccessor( iter, 'seedLength', getSeedLength );
  		setReadWriteAccessor( iter, 'state', getState, setState );
  		setReadOnlyAccessor( iter, 'stateLength', getStateLength );
  		setReadOnlyAccessor( iter, 'byteLength', getStateSize );
  		setReadOnly( iter, 'PRNG', runif.PRNG );
  	}
  	return iter;
  
  	/**
  	* Returns the PRNG seed.
  	*
  	* @private
  	* @returns {PRNGSeedMT19937} seed
  	*/
  	function getSeed() {
  		return runif.seed;
  	}
  
  	/**
  	* Returns the PRNG seed length.
  	*
  	* @private
  	* @returns {PositiveInteger} seed length
  	*/
  	function getSeedLength() {
  		return runif.seedLength;
  	}
  
  	/**
  	* Returns the PRNG state length.
  	*
  	* @private
  	* @returns {PositiveInteger} state length
  	*/
  	function getStateLength() {
  		return runif.stateLength;
  	}
  
  	/**
  	* Returns the PRNG state size (in bytes).
  	*
  	* @private
  	* @returns {PositiveInteger} state size (in bytes)
  	*/
  	function getStateSize() {
  		return runif.byteLength;
  	}
  
  	/**
  	* Returns the current PRNG state.
  	*
  	* @private
  	* @returns {PRNGStateMT19937} current state
  	*/
  	function getState() {
  		return runif.state;
  	}
  
  	/**
  	* Sets the PRNG state.
  	*
  	* @private
  	* @param {PRNGStateMT19937} s - generator state
  	* @throws {Error} must provide a valid state
  	*/
  	function setState( s ) {
  		runif.state = s;
  	}
  
  	/**
  	* Returns an iterator protocol-compliant object containing the next iterated value.
  	*
  	* @private
  	* @returns {Object} iterator protocol-compliant object
  	*/
  	function next() {
  		var out;
  		var v;
  		if ( FLG ) {
  			return {
  				'done': true
  			};
  		}
  		out = {};
  		v = iterator.next();
  		if ( typeof v.value === 'number' ) {
  			out.value = v.value + runif();
  		} else if ( hasOwnProp( v, 'value' ) ) {
  			out.value = NaN;
  		}
  		if ( v.done ) {
  			FLG = true;
  			out.done = true;
  		} else {
  			out.done = false;
  		}
  		return out;
  	}
  
  	/**
  	* 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 iterawun( iterator[ iteratorSymbol ](), sigma, opts );
  	}
  }
  
  
  // EXPORTS //
  
  module.exports = iterawun;
  