area51/lib/random/random-net.js

Experimental prototypes of alien things built in JavaScript. The bits may end up living in a different package.

/**
 * Based upon the code found in https://github.com/dotnet/coreclr/blob/master/src/mscorlib/src/System/Random.cs
 * which is under the MIT License.  
 */

"use strict";

Object.defineProperty(exports, "__esModule", {
	value: true
});
exports["default"] = Random;

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { "default": obj }; }

var _es6SymbolJs = require("../es6/symbol.js");

var _es6SymbolJs2 = _interopRequireDefault(_es6SymbolJs);

var MBIG = 2147483647;
var MSEED = 161803398;
var MZ = 0;

var seedArray = new Array(56);

var internalSample = (0, _es6SymbolJs2["default"])();
var getSampleForLargeRange = (0, _es6SymbolJs2["default"])();

function Random(seed) {
	if (!seed) {
		// closest equivelant to Environment.TickCount
		seed = new Date().getTime();
	}

	this.seedArray = new Array(56);

	seed = seed || new Date().getUTCMilliseconds();
	var seedArray = MSEED - (seed == -2147483648 ? MBIG : Math.abs(seed));
	var num = 1;
	for (var i = 1; i < 55; i++) {
		var num1 = 21 * i % 55;
		this.seedArray[num1] = num;
		num = seedArray - num;
		if (num < 0) num = num + MBIG;

		seedArray = this.seedArray[num1];
	}
	for (var j = 1; j < 5; j++) {
		for (var k = 1; k < 56; k++) {
			this.seedArray[k] = this.seedArray[k] - this.seedArray[1 + (k + 30) % 55];
			if (this.seedArray[k] < 0) this.seedArray[k] = this.seedArray[k] + MBIG;
		}
	}

	this.inext = 0;
	this.inextp = 21;
	seed = 1;
}

;

Random.prototype = {
	next: function next(minValue, maxValue) {
		if (arguments.length === 0) return this[internalSample]();

		if (arguments.length === 1) {
			maxValue = minValue;

			return Math.floor(this.sample() * maxValue);
		}

		var num = maxValue - minValue;
		if (num <= MBIG) {
			return Math.floor(this.sample() * num + minValue);
		}

		return Math.floor(this[getSampleForLargeRange]() * num + minValue);
	},
	nextBytes: function nextBytes(buffer) {
		for (var i = 0; i < buffer.length; i++) {
			buffer[i] = Math.floor(this[internalSample]() % 256);
		}
	},
	nextDouble: function nextDouble() {
		// in doubles have precison of 15 / 16
		var scale = this.sample().toString();
		var slice = scale.substring(0, 16);
		var last = scale[16];
		var next = scale[17];

		if (next >= 5) last++;

		slice = slice + last.toString();

		return parseFloat(slice);
	},
	sample: function sample() {
		return this[internalSample]() * 4.6566128752458e-10;
	}
};

Random.prototype[internalSample] = function () {
	var num = this.inext,
	    num1 = this.inextp,
	    num2 = num + 1;

	num = num2;
	if (num2 >= 56) {
		num = 1;
	}
	var num3 = num1 + 1;
	num1 = num3;
	if (num3 >= 56) {
		num1 = 1;
	}
	var seedArray = this.seedArray[num] - this.seedArray[num1];
	if (seedArray === MBIG) seedArray--;
	if (seedArray < 0) {
		seedArray = seedArray + MBIG;
	}
	this.seedArray[num] = seedArray;
	this.inext = num;
	this.inextp = num1;

	return seedArray;
};

Random.prototype[getSampleForLargeRange] = function () {
	var num = this[internalSample]();
	if (this[internalSample]() % 2 == 0 ? true : false) {
		num = -num;
	}
	return (num + MBIG) / 4294967293;
};
module.exports = exports["default"];