blixt · November 5, 2021 13:42 · Aug 2, 2014 · Aug 2, 2014 · Aug 2, 2014
diff --git a/TestingRNGs.md b/TestingRNGs.md
@@ -44,18 +44,22 @@ Communicating with Dieharder
 ----------------------------
 
 Dieharder can take a file as an input, so we'll use a simple Node.js script for generating a dump of random numbers. See
-`randout.js` below for a template file that implements the simple Park-Miller PRNG.
+`randout.js` below for a template file that implements an integer version of the built-in RNG as well as the very simple
+Park-Miller PRNG.
 
 Make the file executable (`chmod +x randout.js`) then execute it and put its output into a file:
 
 ```
-./randout.js > numbers.txt
+./randout.js > math.random.txt
 ```
 
+**Note:** By default this will create 10,000,000 random numbers. That takes time and space, but is necessary for an accurate
+test.
+
 And now you can test it with Dieharder:
 
 ```
-dieharder -g 202 -f numbers.txt -a
+dieharder -g 202 -f math.random.txt -a
 ```
 
 You can read more about the `dieharder` tool on the [Dieharder homepage][dieharder], but this will run all tests on that file. **Note:** It will take some time!
@@ -64,11 +68,11 @@ You can read more about the `dieharder` tool on the [Dieharder homepage][diehard
 Testing more PRNGs
 ------------------
 
-You can now add more constructors for other PRNGs in `randout.js`. They just need a `random` method which returns a 32-bit
-integer. To change which constructor is used, call the script with the `--prng` argument:
+You can now add more constructors for other PRNGs in `randout.js`. They just need a `next` method which returns an integer.
+To change which constructor is used, call the script with the `--prng` argument:
 
 ```
-./randout.js --prng MersenneTwister > numbers.txt
+./randout.js --prng ParkMiller > park-miller.txt
 ```
 
 

diff --git a/randout.js b/randout.js
@@ -2,18 +2,27 @@
 
 var argv = require('minimist')(process.argv.slice(2));
 
+// 32-bit integer conversion of the built-in RNG.
+function JavaScript() {}
+JavaScript.prototype.next = function () {
+  return Math.random() * 4294967296 >>> 0;
+};
+JavaScript.NUM_BITS = 32;
+
+// Park-Miller.
 function ParkMiller(seed) {
   this._seed = seed % 2147483647;
   if (this._seed <= 0) this._seed += 2147483646;
 }
+ParkMiller.NUM_BITS = 31;
 
 ParkMiller.prototype.next = function () {
   return this._seed = this._seed * 16807 % 2147483647;
 };
 
-var SEED = argv.seed || 1,
-    COUNT = argv.count || 100000,
-    PRNG = argv.prng || 'ParkMiller';
+var SEED = argv.seed || 12345,
+    COUNT = argv.count || 10000000,
+    PRNG = argv.prng || 'JavaScript';
 
 var RandomClass = eval(PRNG);
 if (!RandomClass) {
@@ -24,11 +33,11 @@ process.stdout.write('# ' + PRNG + '\n');
 process.stdout.write('# seed: ' + SEED + '\n');
 process.stdout.write('type: d\n');
 process.stdout.write('count: ' + COUNT + '\n');
-process.stdout.write('numbit: 32\n');
+process.stdout.write('numbit: ' + (RandomClass.NUM_BITS || 32) + '\n');
 
 var r = new RandomClass(SEED);
 for (var i = 0; i < COUNT; i++) {
   var num = r.next().toString();
   num = '          '.slice(0, 10 - num.length) + num;
   process.stdout.write(num + '\n');
-}
+}
diff --git a/TestingRNGs.md b/TestingRNGs.md
@@ -1,5 +1,5 @@
-Testing random number generators with DieHarder
-===============================================
+Testing RNGs with Dieharder
+===========================
 
 This guide is specifically for pseudo-random number generators (PRNGs) written in JavaScript, and tested in Mac OS X.
 
@@ -21,7 +21,7 @@ You can now use Homebrew to install Node.js ([site][nodejs]):
 brew install node
 ```
 
-**DieHarder**  
+**Dieharder**  
 Homebrew also lets you install Dieharder, the tool that tests RNGs ([site][dieharder]):
 
 ```

diff --git a/TestingRNGs.md b/TestingRNGs.md
@@ -0,0 +1,77 @@
+Testing random number generators with DieHarder
+===============================================
+
+This guide is specifically for pseudo-random number generators (PRNGs) written in JavaScript, and tested in Mac OS X.
+
+
+Prerequisites
+-------------
+
+**Homebrew**  
+Run this in the Terminal to install Homebrew ([site][homebrew]):
+
+```
+ruby -e "$(curl -fsSL https://raw.github.com/Homebrew/homebrew/go/install)"
+```
+
+**Node.js**  
+You can now use Homebrew to install Node.js ([site][nodejs]):
+
+```
+brew install node
+```
+
+**DieHarder**  
+Homebrew also lets you install Dieharder, the tool that tests RNGs ([site][dieharder]):
+
+```
+brew install dieharder
+```
+
+**A directory for your testing**  
+Create a directory which you'll use for testing PRNGs. This is where we'll put scripts and data.
+
+**The `minimist` package**  
+A very useful package for parsing arguments which I use for the script below. Go into the testing directory and install it
+with NPM:
+
+```
+npm install minimist
+```
+
+
+Communicating with Dieharder
+----------------------------
+
+Dieharder can take a file as an input, so we'll use a simple Node.js script for generating a dump of random numbers. See
+`randout.js` below for a template file that implements the simple Park-Miller PRNG.
+
+Make the file executable (`chmod +x randout.js`) then execute it and put its output into a file:
+
+```
+./randout.js > numbers.txt
+```
+
+And now you can test it with Dieharder:
+
+```
+dieharder -g 202 -f numbers.txt -a
+```
+
+You can read more about the `dieharder` tool on the [Dieharder homepage][dieharder], but this will run all tests on that file. **Note:** It will take some time!
+
+
+Testing more PRNGs
+------------------
+
+You can now add more constructors for other PRNGs in `randout.js`. They just need a `random` method which returns a 32-bit
+integer. To change which constructor is used, call the script with the `--prng` argument:
+
+```
+./randout.js --prng MersenneTwister > numbers.txt
+```
+
+
+[homebrew]: http://brew.sh/
+[nodejs]: http://nodejs.org/
+[dieharder]: http://www.phy.duke.edu/~rgb/General/dieharder.php
diff --git a/randout.js b/randout.js
@@ -0,0 +1,34 @@
+#!/usr/bin/env node
+
+var argv = require('minimist')(process.argv.slice(2));
+
+function ParkMiller(seed) {
+  this._seed = seed % 2147483647;
+  if (this._seed <= 0) this._seed += 2147483646;
+}
+
+ParkMiller.prototype.next = function () {
+  return this._seed = this._seed * 16807 % 2147483647;
+};
+
+var SEED = argv.seed || 1,
+    COUNT = argv.count || 100000,
+    PRNG = argv.prng || 'ParkMiller';
+
+var RandomClass = eval(PRNG);
+if (!RandomClass) {
+  throw new Error('Invalid PRNG ' + PRNG);
+}
+
+process.stdout.write('# ' + PRNG + '\n');
+process.stdout.write('# seed: ' + SEED + '\n');
+process.stdout.write('type: d\n');
+process.stdout.write('count: ' + COUNT + '\n');
+process.stdout.write('numbit: 32\n');
+
+var r = new RandomClass(SEED);
+for (var i = 0; i < COUNT; i++) {
+  var num = r.next().toString();
+  num = '          '.slice(0, 10 - num.length) + num;
+  process.stdout.write(num + '\n');
+}
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