cs-random.js

/* cs-random.js
 * https://mouseypounds.github.io/stardew-predictor/
 *
 * Simple and incomplete Javascript implementation of the C# pseudo random number generator
 * published at http://referencesource.microsoft.com/#mscorlib/system/random.cs
 */

/*jshint browser: true, jquery: true */

// These would be constants in ES2015
var INT_MIN = -2147483648,
	INT_MAX = 2147483647,
	MBIG = INT_MAX,
	MSEED = 161803398;

function CSRandom(Seed) {
	"use strict";
	var ii, mj, mk, i, k, subtraction;

	// Alternative to default argument
	if (typeof(Seed) === 'undefined') {
		Seed = Date.getTime();
	}
	Seed = parseInt(Seed); // Force an integer since there is no type checking

	this.inext = 0;
	this.inextp = 0;
	this.SeedArray = [];

	subtraction = (Seed === INT_MIN) ? INT_MAX : Math.abs(Seed);
	mj = MSEED - subtraction;
	this.SeedArray[55] = mj;
	mk = 1;
	for (i = 1; i < 55; i++) {
		ii = (21 * i) % 55;
		this.SeedArray[ii] = mk;
		mk = mj - mk;
		if (mk < 0) {
			mk += MBIG;
		}
		mj = this.SeedArray[ii];
	}
	for (k = 1; k < 5; k++) {
		for (i = 1; i < 56; i++) {
			this.SeedArray[i] -= this.SeedArray[1 + (i + 30) % 55];
			if (this.SeedArray[i] > INT_MAX) {
				this.SeedArray[i] -= (Math.abs(INT_MIN) + INT_MAX);
			}
			if (this.SeedArray[i] < 0) {
				this.SeedArray[i] += MBIG;
			}
		}
	}
	this.inext = 0;
	this.inextp = 21;
	Seed = 1;
}

CSRandom.prototype.Sample = function() {
	"use strict";
	return parseFloat(this.InternalSample() * (1.0 / MBIG));
};

CSRandom.prototype.InternalSample = function() {
	"use strict";
	var retVal,
		locINext = this.inext,
		locINextp = this.inextp;

	if (++locINext >= 56) {
		locINext = 1;
	}
	if (++locINextp >= 56) {
		locINextp = 1;
	}
	retVal = this.SeedArray[locINext] - this.SeedArray[locINextp];
	if (retVal === MBIG) {
		retVal--;
	}
	if (retVal < 0) {
		retVal += MBIG;
	}
	this.SeedArray[locINext] = retVal;
	this.inext = locINext;
	this.inextp = locINextp;
	return parseInt(retVal);
};

CSRandom.prototype.GetSampleForLargeRange = function() {
	"use strict";
	// This might require special large integer handling
	var result = this.InternalSample(),
		d;

	if (this.InternalSample() %2 === 0) {
		result = -result;
	}
	d = result;
	d += (INT_MAX - 1);
	d /= 2 * INT_MAX - 1;
	return d;
};

CSRandom.prototype.Next = function(a, b) {
	"use strict";
	// Next() gives range of [0..INT_MAX)
	// Next(a) gives range of [0..a)
	// Next(a,b) gives range of [a..b)
	var min = 0,
		max = INT_MAX,
		range;

	if (typeof b !== 'undefined') {
		// 2 parameter version
		max = b;
		min = (typeof a !== 'undefined') ? a : 0;
		if (min > max) {
			throw "Argument out of range - min (" + min + ") should be smaller than max (" + max + ")";
		}
		range = max - min;
		if (range <= INT_MAX) {
			return parseInt(this.Sample() * range + min);
		} else {
			return parseInt(this.GetSampleForLargeRange() * range + min);
		}
	} else if (typeof a !== 'undefined') {
		// 1 parameter version
		max = a;
		if (max < 0) {
			throw "Argument out of range - max (" + max + ") must be positive";
		}
		return parseInt(this.Sample() * max);
	} else {
		return this.InternalSample();
	}
};

CSRandom.prototype.NextDouble = function() {
	"use strict";
	return this.Sample();
};

// not implementing NextBytes since Stardew Valley doesn't use it