Skip to content

Instantly share code, notes, and snippets.

@leegrey
Created August 3, 2012 13:32
Show Gist options
  • Star 1 You must be signed in to star a gist
  • Fork 0 You must be signed in to fork a gist
  • Save leegrey/3247732 to your computer and use it in GitHub Desktop.
Save leegrey/3247732 to your computer and use it in GitHub Desktop.
Seeded random in Javascript, translated from Michael Baczynski's AS2 ( http://www.polygonal.de )
/*
* Copyright (c) 2009 Michael Baczynski, http://www.polygonal.de
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
/**
* Implementation of the Park Miller (1988) "minimal standard" linear
* congruential pseudo-random number generator.
*
* For a full explanation visit: http://www.firstpr.com.au/dsp/rand31/
*
* The generator uses a modulus constant (m) of 2^31 - 1 which is a
* Mersenne Prime number and a full-period-multiplier of 16807.
* Output is a 31 bit unsigned integer. The range of values output is
* 1 to 2,147,483,646 (2^31-1) and the seed must be in this range too.
*
* David G. Carta's optimisation which needs only 32 bit integer math,
* and no division is actually *slower* in flash (both AS2 & AS3) so
* it's better to use the double-precision floating point version.
*
* @author Michael Baczynski, www.polygonal.de
.............................................................................
Converted to JavaScript by Lee Grey, Aug 3rd 2012
*/
/**
* set seed with a 31 bit unsigned integer
* between 1 and 0X7FFFFFFE inclusive. don't use 0!
*/
SeedRND = new SeededRandomNumberGenerator(); //global object
function SeededRandomNumberGenerator() {}
SeededRandomNumberGenerator.prototype.seed = 1337;
/**
* provides the next pseudorandom number
* as an unsigned integer (31 bits)
*/
SeededRandomNumberGenerator.prototype.randomInt = function()
{
return this.gen();
}
/**
* provides the next pseudorandom number
* as a float between nearly 0 and nearly 1.0.
*/
SeededRandomNumberGenerator.prototype.random = function()
{
return ( this.gen() / 2147483647 );
}
/**
* provides the next pseudorandom number
* as an unsigned integer (31 bits) betweeen
* a given range.
*/
SeededRandomNumberGenerator.prototype.randomIntRange = function(min, max)
{
min -= .4999;
max += .4999;
return Math.round(min + ((max - min) * this.random()));
}
/**
* provides the next pseudorandom number
* as a float between a given range.
*/
SeededRandomNumberGenerator.prototype.randomRange = function(min, max)
{
return min + ((max - min) * this.random());
}
/**
* generator:
* new-value = (old-value * 16807) mod (2^31 - 1)
*/
SeededRandomNumberGenerator.prototype.gen = function()
{
//integer version 1, for max int 2^46 - 1 or larger.
return this.seed = (this.seed * 16807) % 2147483647;
/**
* integer version 2, for max int 2^31 - 1 (slowest)
*/
//var test:int = 16807 * (seed % 127773 >> 0) - 2836 * (seed / 127773 >> 0);
//return seed = (test > 0 ? test : test + 2147483647);
/**
* david g. carta's optimisation is 15% slower than integer version 1
*/
//var hi:Number = 16807 * (seed >> 16);
//var lo:Number = 16807 * (seed & 0xFFFF) + ((hi & 0x7FFF) << 16) + (hi >> 15);
//return seed = (lo > 0x7FFFFFFF ? lo - 0x7FFFFFFF : lo);
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment