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@Protonk Protonk/prng.js
Last active Oct 18, 2019

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Various PRNGs, implemented in javascript.
// Linear Congruential Generator
// Variant of a Lehman Generator
var lcg = (function() {
// Set to values from http://en.wikipedia.org/wiki/Numerical_Recipes
// m is basically chosen to be large (as it is the max period)
// and for its relationships to a and c
var m = 4294967296,
// a - 1 should be divisible by m's prime factors
a = 1664525,
// c and m should be co-prime
c = 1013904223,
seed, z;
return {
setSeed : function(val) {
z = seed = val || Math.round(Math.random() * m);
},
getSeed : function() {
return seed;
},
rand : function() {
// define the recurrence relationship
z = (a * z + c) % m;
// return a float in [0, 1)
// if z = m then z / m = 0 therefore (z % m) / m < 1 always
return z / m;
}
};
}());
// Complementary Multiply-With-Carry of lag 1
// similar to Chrome's implementation (structured more traditionally)
var mwc = (function() {
// Set two seed values.
var carry, x,
// Value of modulus and multiplier are chosen together
// 2^32 is chosen because it's similar to the others
// but we don't use bitwise operations to take advantage of this
max = Math.pow(2, 32),
a = 3636507990;
return {
setSeed : function(arr) {
var seed = arr || [0,1].map(function() {
return Math.round(Math.random() * max);
});
carry = seed[0];
x = seed[1];
},
getSeed : function() {
return [carry, x];
},
rand : function() {
// Two multiplications
// create carry with division, x with mod
// The first part is the "carry" where we're
// using both parts of the residue
carry = ((a * x) + carry) / max;
// subtracting from the max is what makes it the compliment
x = (max - 1) - ((a * x) + carry) % max;
return x / max;
}
};
}());
// 16 bit Linear feedback shift register
var lfsr = (function(){
var max = Math.pow(2, 16),
period = 0,
seed, out;
return {
setSeed : function(val) {
out = seed = val || Math.round(Math.random() * max);
},
getSeed : function() {
return seed;
},
getPeriod : function() {
return period;
},
rand : function() {
var bit;
// From http://en.wikipedia.org/wiki/Linear_feedback_shift_register
bit = ((out >> 0) ^ (out >> 2) ^ (out >> 3) ^ (out >> 5) ) & 1;
out = (out >> 1) | (bit << 15);
period++;
return out / max;
}
};
}());
//Webkit2's crazy invertible mapping generator
var invwk = (function() {
var max = Math.pow(2, 32),
seed;
return {
setSeed : function(val) {
seed = val || Math.round(Math.random() * max);
},
getSeed : function() {
return seed;
},
rand : function() {
// creates randomness...somehow...
seed += (seed * seed) | 5;
// Shift off bits, discarding the sign. Discarding the sign is
// important because OR w/ 5 can give us + or - numbers.
return (seed >>> 32) / max;
}
};
}());
// von Neumann's middle square
// This is a terrible generator, never use it
var middlesq = (function() {
var seed = 4563;
return {
setSeed : function(val) {
seed = val || Math.round(Math.random() * 99980001);
},
rand : function () {
// Square the seed, pad to 8 digits
var middle = (seed * seed).toString();
while(middle.length < 8) {
middle = "0" + middle;
}
// Select the middle 4 digits as the new
// seed
seed = parseInt(middle.slice(2, 6), 10);
// return a number on [0, 1)
return seed / 10000;
}
};
}());
@JamesJansson

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JamesJansson commented Jul 10, 2014

Thinking of using the LCG in an open source mathematical model, what license is this?

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