isaac.js

/*
 isaac.js Copyright (c) 2012 Yves-Marie K. Rinquin
 
 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.
 */

/* isaac module pattern */
var isaac = (function(){

    /* internal states */
    var m = Array(256), // internal memory
        acc = 0,        // accumulator
        brs = 0,        // last result
        cnt = 0,        // counter
        r = Array(256), // result array
        gnt = 0,        // generation counter
        isd = false;    // initially seeded


    /* 32-bit integer safe adder */
    function add(x, y) {
        var lsb = (x & 0xffff) + (y & 0xffff),
            msb = (x >>>   16) + (y >>>   16) + (lsb >>> 16);
        return (msb << 16) | (lsb & 0xffff);
    }

    /* initialisation */
    function reset() {
        acc = brs = cnt = 0;
        for (var i = 0; i < 256; ++i)
            m[i] = r[i] = 0;
        gnt = 0;
    }

    /* seeding function */
    function seed(s) {
        var a, b, c, d, e, f, g, h, i;

        /* seeding the seeds of love */
        a = b = c = d = e = f = g = h = 0x9e3779b9; /* the golden ratio */

        if (s && typeof(s) === 'number')
            s = [s];

        if (s instanceof Array) {
            reset();
            for (i = 0; i < s.length; ++i)
                r[i & 0xff] += typeof(s[i]) === 'number' ? s[i] : 0;
        }

        /* private: seed mixer */
        function seed_mix() {
            a ^= b <<  11; d = add(d, a); b = add(b, c);
            b ^= c >>>  2; e = add(e, b); c = add(c, d);
            c ^= d <<   8; f = add(f, c); d = add(d, e);
            d ^= e >>> 16; g = add(g, d); e = add(e, f);
            e ^= f <<  10; h = add(h, e); f = add(f, g);
            f ^= g >>>  4; a = add(a, f); g = add(g, h);
            g ^= h <<   8; b = add(b, g); h = add(h, a);
            h ^= a >>>  9; c = add(c, h); a = add(a, b);
        }

        for (i = 0; i < 4; i++) /* scramble it */
            seed_mix();

        for (i = 0; i < 256; i += 8) {
            if (s) /* use all the information in the seed */
                a = add(a, r[i + 0]), b = add(b, r[i + 1]),
                c = add(c, r[i + 2]), d = add(d, r[i + 3]),
                e = add(e, r[i + 4]), f = add(f, r[i + 5]),
                g = add(g, r[i + 6]), h = add(h, r[i + 7]);
            seed_mix();
            /* fill in m[] with messy stuff */
            m[i + 0] = a; m[i + 1] = b; m[i + 2] = c; m[i + 3] = d;
            m[i + 4] = e; m[i + 5] = f; m[i + 6] = g; m[i + 7] = h;
        }
        if (s)
            /* do a second pass to make all of the seed affect all of m[] */
            for (i = 0; i < 256; i += 8)
                a = add(a, m[i + 0]), b = add(b, m[i + 1]),
                c = add(c, m[i + 2]), d = add(d, m[i + 3]),
                e = add(e, m[i + 4]), f = add(f, m[i + 5]),
                g = add(g, m[i + 6]), h = add(h, m[i + 7]),
                seed_mix(),
                /* fill in m[] with messy stuff (again) */
                m[i + 0] = a, m[i + 1] = b, m[i + 2] = c, m[i + 3] = d,
                m[i + 4] = e, m[i + 5] = f, m[i + 6] = g, m[i + 7] = h;
        prng(); /* fill in the first set of results */
        gnt = 256;  /* prepare to use the first set of results */;
    }

    /* isaac generator, n = number of run */
    function prng(n) {
        var i, x, y;
        n = n && typeof(n) === 'number' ? Math.abs(Math.floor(n)) : 1;
        while (n--) {
            cnt = add(cnt,   1);
            brs = add(brs, cnt);
            for(i = 0; i < 256; i++) {
                switch(i & 3) {
                    case 0: acc ^= acc <<  13; break;
                    case 1: acc ^= acc >>>  6; break;
                    case 2: acc ^= acc <<   2; break;
                    case 3: acc ^= acc >>> 16; break;
                }
                acc        = add(m[(i +  128) & 0xff], acc); x = m[i];
                m[i] =   y = add(m[(x >>>  2) & 0xff], add(acc, brs));
                r[i] = brs = add(m[(y >>> 10) & 0xff], x);
            }
        }
    }

    /* return a random number between */
    return function() {
        if (!isd) // seed from accumulator
            isd = true,
            accum.stop(),
            seed(accum.fetch());
        if (!gnt--)
            prng(), gnt = 255;
        return r[gnt];
    };
})();