mafalda-api/game/machine/generator.js

function Ziggurat(seeder = 123456789){

    var jsr = seeder;

    var wn = Array(128);
    var fn = Array(128);
    var kn = Array(128);

    function RNOR(){
        var hz = SHR3();
        var iz = hz & 127;
        return (Math.abs(hz) < kn[iz]) ? hz * wn[iz] : nfix(hz, iz);
    }

    this.nextGaussian = function(){
        return RNOR();
    };

    function nfix(hz, iz){
        var r = 3.442619855899;
        var r1 = 1.0 / r;
        var x;
        var y;
        while(true){
            x = hz * wn[iz];
            if( iz === 0 ){
                x = (-Math.log(UNI()) * r1); 
                y = -Math.log(UNI());
                while( y + y < x * x){
                    x = (-Math.log(UNI()) * r1); 
                    y = -Math.log(UNI());
                }
                return ( hz > 0 ) ? r+x : -r-x;
            }

            if( fn[iz] + UNI() * (fn[iz-1] - fn[iz]) < Math.exp(-0.5 * x * x) ){
                return x;
            }
            hz = SHR3();
            iz = hz & 127;
 
            if( Math.abs(hz) < kn[iz]){
                return (hz * wn[iz]);
            }
        }
    }

    function SHR3(){
        var jz = jsr;
        var jzr = jsr;
        jzr ^= (jzr << 13);
        jzr ^= (jzr >>> 17);
        jzr ^= (jzr << 5);
        jsr = jzr;
        return (jz+jzr) | 0;
    }

    function UNI(){
        return 0.5 * (1 + SHR3() / -Math.pow(2,31));
    }

    function zigset(){
    // seed generator based on current time
    //jsr ^= new Date().getTime();

        var m1 = 2147483648.0;
        var dn = 3.442619855899;
        var tn = dn;
        var vn = 9.91256303526217e-3;
    
        var q = vn / Math.exp(-0.5 * dn * dn);
        kn[0] = Math.floor((dn/q)*m1);
        kn[1] = 0;

        wn[0] = q / m1;
        wn[127] = dn / m1;

        fn[0] = 1.0;
        fn[127] = Math.exp(-0.5 * dn * dn);

        for(var i = 126; i >= 1; i--){
            dn = Math.sqrt(-2.0 * Math.log( vn / dn + Math.exp( -0.5 * dn * dn)));
            kn[i+1] = Math.floor((dn/tn)*m1);
            tn = dn;
            fn[i] = Math.exp(-0.5 * dn * dn);
            wn[i] = dn / m1;
        }
    }
    zigset();
}

module.exports = Ziggurat;