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February 10, 2010 16:24
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a Mersenne Twister implementation in javascript. Makes up for Math.random() not letting you specify a seed value.
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| /* | |
| I've wrapped Makoto Matsumoto and Takuji Nishimura's code in a namespace | |
| so it's better encapsulated. Now you can have multiple random number generators | |
| and they won't stomp all over eachother's state. | |
| If you want to use this as a substitute for Math.random(), use the random() | |
| method like so: | |
| var m = new MersenneTwister(); | |
| var randomNumber = m.random(); | |
| You can also call the other genrand_{foo}() methods on the instance. | |
| If you want to use a specific seed in order to get a repeatable random | |
| sequence, pass an integer into the constructor: | |
| var m = new MersenneTwister(123); | |
| and that will always produce the same random sequence. | |
| Sean McCullough (banksean@gmail.com) | |
| */ | |
| /* | |
| A C-program for MT19937, with initialization improved 2002/1/26. | |
| Coded by Takuji Nishimura and Makoto Matsumoto. | |
| Before using, initialize the state by using init_genrand(seed) | |
| or init_by_array(init_key, key_length). | |
| Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura, | |
| All rights reserved. | |
| Redistribution and use in source and binary forms, with or without | |
| modification, are permitted provided that the following conditions | |
| are met: | |
| 1. Redistributions of source code must retain the above copyright | |
| notice, this list of conditions and the following disclaimer. | |
| 2. Redistributions in binary form must reproduce the above copyright | |
| notice, this list of conditions and the following disclaimer in the | |
| documentation and/or other materials provided with the distribution. | |
| 3. The names of its contributors may not be used to endorse or promote | |
| products derived from this software without specific prior written | |
| permission. | |
| THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
| "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
| LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
| A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR | |
| CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, | |
| EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, | |
| PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR | |
| PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF | |
| LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING | |
| NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS | |
| SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
| Any feedback is very welcome. | |
| http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html | |
| email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space) | |
| */ | |
| var MersenneTwister = function(seed) { | |
| if (seed == undefined) { | |
| seed = new Date().getTime(); | |
| } | |
| /* Period parameters */ | |
| this.N = 624; | |
| this.M = 397; | |
| this.MATRIX_A = 0x9908b0df; /* constant vector a */ | |
| this.UPPER_MASK = 0x80000000; /* most significant w-r bits */ | |
| this.LOWER_MASK = 0x7fffffff; /* least significant r bits */ | |
| this.mt = new Array(this.N); /* the array for the state vector */ | |
| this.mti=this.N+1; /* mti==N+1 means mt[N] is not initialized */ | |
| this.init_genrand(seed); | |
| } | |
| /* initializes mt[N] with a seed */ | |
| MersenneTwister.prototype.init_genrand = function(s) { | |
| this.mt[0] = s >>> 0; | |
| for (this.mti=1; this.mti<this.N; this.mti++) { | |
| var s = this.mt[this.mti-1] ^ (this.mt[this.mti-1] >>> 30); | |
| this.mt[this.mti] = (((((s & 0xffff0000) >>> 16) * 1812433253) << 16) + (s & 0x0000ffff) * 1812433253) | |
| + this.mti; | |
| /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */ | |
| /* In the previous versions, MSBs of the seed affect */ | |
| /* only MSBs of the array mt[]. */ | |
| /* 2002/01/09 modified by Makoto Matsumoto */ | |
| this.mt[this.mti] >>>= 0; | |
| /* for >32 bit machines */ | |
| } | |
| } | |
| /* initialize by an array with array-length */ | |
| /* init_key is the array for initializing keys */ | |
| /* key_length is its length */ | |
| /* slight change for C++, 2004/2/26 */ | |
| MersenneTwister.prototype.init_by_array = function(init_key, key_length) { | |
| var i, j, k; | |
| this.init_genrand(19650218); | |
| i=1; j=0; | |
| k = (this.N>key_length ? this.N : key_length); | |
| for (; k; k--) { | |
| var s = this.mt[i-1] ^ (this.mt[i-1] >>> 30) | |
| this.mt[i] = (this.mt[i] ^ (((((s & 0xffff0000) >>> 16) * 1664525) << 16) + ((s & 0x0000ffff) * 1664525))) | |
| + init_key[j] + j; /* non linear */ | |
| this.mt[i] >>>= 0; /* for WORDSIZE > 32 machines */ | |
| i++; j++; | |
| if (i>=this.N) { this.mt[0] = this.mt[this.N-1]; i=1; } | |
| if (j>=key_length) j=0; | |
| } | |
| for (k=this.N-1; k; k--) { | |
| var s = this.mt[i-1] ^ (this.mt[i-1] >>> 30); | |
| this.mt[i] = (this.mt[i] ^ (((((s & 0xffff0000) >>> 16) * 1566083941) << 16) + (s & 0x0000ffff) * 1566083941)) | |
| - i; /* non linear */ | |
| this.mt[i] >>>= 0; /* for WORDSIZE > 32 machines */ | |
| i++; | |
| if (i>=this.N) { this.mt[0] = this.mt[this.N-1]; i=1; } | |
| } | |
| this.mt[0] = 0x80000000; /* MSB is 1; assuring non-zero initial array */ | |
| } | |
| /* generates a random number on [0,0xffffffff]-interval */ | |
| MersenneTwister.prototype.genrand_int32 = function() { | |
| var y; | |
| var mag01 = new Array(0x0, this.MATRIX_A); | |
| /* mag01[x] = x * MATRIX_A for x=0,1 */ | |
| if (this.mti >= this.N) { /* generate N words at one time */ | |
| var kk; | |
| if (this.mti == this.N+1) /* if init_genrand() has not been called, */ | |
| this.init_genrand(5489); /* a default initial seed is used */ | |
| for (kk=0;kk<this.N-this.M;kk++) { | |
| y = (this.mt[kk]&this.UPPER_MASK)|(this.mt[kk+1]&this.LOWER_MASK); | |
| this.mt[kk] = this.mt[kk+this.M] ^ (y >>> 1) ^ mag01[y & 0x1]; | |
| } | |
| for (;kk<this.N-1;kk++) { | |
| y = (this.mt[kk]&this.UPPER_MASK)|(this.mt[kk+1]&this.LOWER_MASK); | |
| this.mt[kk] = this.mt[kk+(this.M-this.N)] ^ (y >>> 1) ^ mag01[y & 0x1]; | |
| } | |
| y = (this.mt[this.N-1]&this.UPPER_MASK)|(this.mt[0]&this.LOWER_MASK); | |
| this.mt[this.N-1] = this.mt[this.M-1] ^ (y >>> 1) ^ mag01[y & 0x1]; | |
| this.mti = 0; | |
| } | |
| y = this.mt[this.mti++]; | |
| /* Tempering */ | |
| y ^= (y >>> 11); | |
| y ^= (y << 7) & 0x9d2c5680; | |
| y ^= (y << 15) & 0xefc60000; | |
| y ^= (y >>> 18); | |
| return y >>> 0; | |
| } | |
| /* generates a random number on [0,0x7fffffff]-interval */ | |
| MersenneTwister.prototype.genrand_int31 = function() { | |
| return (this.genrand_int32()>>>1); | |
| } | |
| /* generates a random number on [0,1]-real-interval */ | |
| MersenneTwister.prototype.genrand_real1 = function() { | |
| return this.genrand_int32()*(1.0/4294967295.0); | |
| /* divided by 2^32-1 */ | |
| } | |
| /* generates a random number on [0,1)-real-interval */ | |
| MersenneTwister.prototype.random = function() { | |
| return this.genrand_int32()*(1.0/4294967296.0); | |
| /* divided by 2^32 */ | |
| } | |
| /* generates a random number on (0,1)-real-interval */ | |
| MersenneTwister.prototype.genrand_real3 = function() { | |
| return (this.genrand_int32() + 0.5)*(1.0/4294967296.0); | |
| /* divided by 2^32 */ | |
| } | |
| /* generates a random number on [0,1) with 53-bit resolution*/ | |
| MersenneTwister.prototype.genrand_res53 = function() { | |
| var a=this.genrand_int32()>>>5, b=this.genrand_int32()>>>6; | |
| return(a*67108864.0+b)*(1.0/9007199254740992.0); | |
| } | |
| /* These real versions are due to Isaku Wada, 2002/01/09 added */ |
I created a little test chart here: https://jsfiddle.net/mika76/vu5nsdLo/
guys, keep in mind that while it most probably get reasonable results overall, it would not return the same result as C version. I'm trying to implement cross platform twister that will behave exactly the same on server & browser and it never do. 3 hours of debugging lead me to the step where init_genrand makes * 1812433253 and when we have high enough numbers it leads to JavaScript number double precision loss issue:
So, I'll try to use new bigint type... and I hope it have polyfill:
console.log(1812433253n * 2244851808n); // 4068644064876371424n
console.log((1812433253n * 2244851808n) % (1n<<32n)); // 1819614688n
ah, just noted your beautiful solution by splitting 's' on hi/lo mask group. This is much easier, thanks.
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I've wrapped this code into a npm module long time ago, thanks for implementation!
https://github.com/boo1ean/mersenne-twister