From 194e1a8896067b929315a603acad2e750dfa1526 Mon Sep 17 00:00:00 2001
From: Charles Lowell <cowboyd@frontside.io>
Date: Wed, 24 Mar 2021 16:10:13 +0200
Subject: Give each faker instance its own random number generator

Currently, every Faker instance shares the same random number
generator instance which means that to seed one faker instance is to
seed them all. This can result in duplicate data being generated all
over the place.

This just extracts the public API of the mersenne twister found in
`vendor/mersenne.js` and creates a single instance of it per
faker.

This implementation is a tad sub-optimal since calling `seed()` on
a faker instance will result in two redundant calls to
`mersenne.init_genrand()`: one in `random.js` and the other in
`datatype.js`. It would probably be more DRY to create the mersenne
instance once in faker and then pass it into to the `Random` and
`Datatype` instances, however, this takes the strategy of the smallest
possible API change.
---
 lib/datatype.js |  8 +++-----
 lib/index.js    |  3 +++
 lib/mersenne.js | 31 +++++++++++++++++++++++++++++++
 lib/random.js   |  6 ++----
 4 files changed, 39 insertions(+), 9 deletions(-)
 create mode 100644 lib/mersenne.js

(limited to 'lib')

diff --git a/lib/datatype.js b/lib/datatype.js
index d2ec9ad2..02ea3759 100644
--- a/lib/datatype.js
+++ b/lib/datatype.js
@@ -1,5 +1,3 @@
-var mersenne = require('../vendor/mersenne');
-
 /**
  *
  * @namespace faker.datatype
@@ -7,10 +5,10 @@ var mersenne = require('../vendor/mersenne');
 function Datatype (faker, seed) {
   // Use a user provided seed if it is an array or number
   if (Array.isArray(seed) && seed.length) {
-    mersenne.seed_array(seed);
+    faker.mersenne.seed_array(seed);
   }
   else if(!isNaN(seed)) {
-    mersenne.seed(seed);
+    faker.mersenne.seed(seed);
   }
 
   /**
@@ -47,7 +45,7 @@ function Datatype (faker, seed) {
     }
 
     var randomNumber = Math.floor(
-      mersenne.rand(max / options.precision, options.min / options.precision));
+      faker.mersenne.rand(max / options.precision, options.min / options.precision));
     // Workaround problem in Float point arithmetics for e.g. 6681493 / 0.01
     randomNumber = randomNumber / (1 / options.precision);
 
diff --git a/lib/index.js b/lib/index.js
index f76a581e..a80580bd 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -92,6 +92,9 @@ function Faker (opts) {
   var Unique = require('./unique');
   self.unique = new Unique(self).unique;
 
+  var Mersenne = require('./mersenne');
+  self.mersenne = new Mersenne();
+
   var Random = require('./random');
   self.random = new Random(self);
 
diff --git a/lib/mersenne.js b/lib/mersenne.js
new file mode 100644
index 00000000..722ebc46
--- /dev/null
+++ b/lib/mersenne.js
@@ -0,0 +1,31 @@
+var Gen = require('../vendor/mersenne').MersenneTwister19937;
+
+function Mersenne() {
+  var gen = new Gen();
+  gen.init_genrand((new Date).getTime() % 1000000000);
+
+  this.rand = function(max, min) {
+    if (max === undefined)
+    {
+      min = 0;
+      max = 32768;
+    }
+    return Math.floor(gen.genrand_real2() * (max - min) + min);
+  }
+  this.seed = function(S) {
+    if (typeof(S) != 'number')
+    {
+      throw new Error("seed(S) must take numeric argument; is " + typeof(S));
+    }
+    gen.init_genrand(S);
+  }
+  this.seed_array = function(A) {
+    if (typeof(A) != 'object')
+    {
+      throw new Error("seed_array(A) must take array of numbers; is " + typeof(A));
+    }
+    gen.init_by_array(A, A.length);
+  }
+}
+
+module.exports = Mersenne;
diff --git a/lib/random.js b/lib/random.js
index 4c2daaac..4443c555 100644
--- a/lib/random.js
+++ b/lib/random.js
@@ -1,5 +1,3 @@
-var mersenne = require('../vendor/mersenne');
-
 /**
  * Method to reduce array of characters
  * @param arr existing array of characters
@@ -22,10 +20,10 @@ var arrayRemove = function (arr, values) {
 function Random (faker, seed) {
   // Use a user provided seed if it is an array or number
   if (Array.isArray(seed) && seed.length) {
-    mersenne.seed_array(seed);
+    faker.mersenne.seed_array(seed);
   }
   else if(!isNaN(seed)) {
-    mersenne.seed(seed);
+    faker.mersenne.seed(seed);
   }
 
   /**
-- 
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