gistfile1.txt

    static readonly Func<Constants,Variable,Variable> bigrand_d = bigrand;
    [ImplicitConsts] public static Variable bigrand(Constants c, Variable a1) {
        int r1;
        P6any o1 = a1.Fetch();
        if (!o1.mo.is_any)
            return HandleSpecial1(c, a1, o1, bigrand_d);
        P6any n1 = GetNumber(a1, o1, out r1);

        BigInteger top = PromoteToBigInt(r1, n1);
        int bits = (int) Math.Ceiling(BigInteger.Log(top, 2));
        int bytes = bits / 8 + 1;
        byte mask = 0;
        switch(bits % 8) {
            case 0: mask = 255; break;
            case 1: mask = 1; break;
            case 2: mask = 3; break;
            case 3: mask = 7; break;
            case 4: mask = 15; break;
            case 5: mask = 31; break;
            case 6: mask = 63; break;
            case 7: mask = 127; break;
        }

        Random rnd = new Random();
        Byte[] b = new Byte[bytes + 1];
        while (true) {
            rnd.NextBytes(b);
            b[bytes] = 0;
            b[bytes - 1] &= mask;
            BigInteger candidate = new BigInteger (b);
            if (candidate < top)
                return MakeInt(candidate);
        }
    }