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POIs this a "good enough" random algorithm; why isn't it used if it's faster?
 

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  1. POIs this a "good enough" random algorithm; why isn't it used if it's faster?
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    <p>I made a class called <code>QuickRandom</code>, and its job is to produce random numbers quickly. It's really simple: just take the old value, multiply by a <code>double</code>, and take the decimal part.</p> <p>Here is my <code>QuickRandom</code> class in its entirety:</p> <pre><code>public class QuickRandom { private double prevNum; private double magicNumber; public QuickRandom(double seed1, double seed2) { if (seed1 &gt;= 1 || seed1 &lt; 0) throw new IllegalArgumentException("Seed 1 must be &gt;= 0 and &lt; 1, not " + seed1); prevNum = seed1; if (seed2 &lt;= 1 || seed2 &gt; 10) throw new IllegalArgumentException("Seed 2 must be &gt; 1 and &lt;= 10, not " + seed2); magicNumber = seed2; } public QuickRandom() { this(Math.random(), Math.random() * 10); } public double random() { return prevNum = (prevNum*magicNumber)%1; } } </code></pre> <p>And here is the code I wrote to test it:</p> <pre><code>public static void main(String[] args) { QuickRandom qr = new QuickRandom(); /*for (int i = 0; i &lt; 20; i ++) { System.out.println(qr.random()); }*/ //Warm up for (int i = 0; i &lt; 10000000; i ++) { Math.random(); qr.random(); System.nanoTime(); } long oldTime; oldTime = System.nanoTime(); for (int i = 0; i &lt; 100000000; i ++) { Math.random(); } System.out.println(System.nanoTime() - oldTime); oldTime = System.nanoTime(); for (int i = 0; i &lt; 100000000; i ++) { qr.random(); } System.out.println(System.nanoTime() - oldTime); } </code></pre> <p>It is a very simple algorithm that simply multiplies the previous double by a "magic number" double. I threw it together pretty quickly, so I could probably make it better, but strangely, it seems to be working fine.</p> <p>This is sample output of the commented-out lines in the <code>main</code> method:</p> <pre><code>0.612201846732229 0.5823974655091941 0.31062451498865684 0.8324473610354004 0.5907187526770246 0.38650264675748947 0.5243464344127049 0.7812828761272188 0.12417247811074805 0.1322738256858378 0.20614642573072284 0.8797579436677381 0.022122999476108518 0.2017298328387873 0.8394849894162446 0.6548917685640614 0.971667953190428 0.8602096647696964 0.8438709031160894 0.694884972852229 </code></pre> <p>Hm. Pretty random. In fact, that would work for a random number generator in a game.</p> <p>Here is sample output of the non-commented out part:</p> <pre><code>5456313909 1427223941 </code></pre> <p>Wow! It performs almost 4 times faster than <code>Math.random</code>.</p> <p>I remember reading somewhere that <code>Math.random</code> used <code>System.nanoTime()</code> and tons of crazy modulus and division stuff. Is that really necessary? My algorithm performs a lot faster and it seems pretty random.</p> <p>I have two questions:</p> <ul> <li>Is my algorithm "good enough" (for, say, a game, where <strong>really</strong> random numbers aren't too important)?</li> <li>Why does <code>Math.random</code> do so much when it seems just simple multiplication and cutting out the decimal will suffice?</li> </ul>
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      1. POIs this a "good enough" random algorithm; why isn't it used if it's faster?
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    1. CO"seems pretty random"; you should generate a histogram and run some autocorrelation on your sequence...
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      1. POIs this a "good enough" random algorithm; why isn't it used if it's faster?
      1. USOliver Charlesworth
    2. CO@OliCharlesworth I... err... what? I have no idea what you just said :P
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      1. POIs this a "good enough" random algorithm; why isn't it used if it's faster?
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    3. COHe means "seems pretty random" isn't really an objective measure of randomness and you should get some actual statistics.
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      1. USMatt H
 

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